Tag Archives: astronomy

The system Kepler-444 formed when the Milky Way galaxy was a youthful two billion years old. The planets were detected from the dimming that occurs when they transit the disc of their parent star, as shown in this artist's conception.

Image courtesy of NASA

Circular orbits identified for 74 small exoplanets

Observations of 74 Earth-sized planets around distant stars may narrow field of habitable candidates.

By Jennifer Chu


CAMBRIDGE, Mass. – Viewed from above, our solar system’s planetary orbits around the sun resemble rings around a bulls-eye. Each planet, including Earth, keeps to a roughly circular path, always maintaining the same distance from the sun.

The system Kepler-444 formed when the Milky Way galaxy was a youthful two billion years old. The planets were detected from the dimming that occurs when they transit the disc of their parent star, as shown in this artist's conception. Image courtesy of NASA
The system Kepler-444 formed when the Milky Way galaxy was a youthful two billion years old. The planets were detected from the dimming that occurs when they transit the disc of their parent star, as shown in this artist’s conception.
Image courtesy of NASA

For decades, astronomers have wondered whether the solar system’s circular orbits might be a rarity in our universe. Now a new analysis suggests that such orbital regularity is instead the norm, at least for systems with planets as small as Earth.

In a paper published in the Astrophysical Journal, researchers from MIT and Aarhus University in Denmark report that 74 exoplanets, located hundreds of light-years away, orbit their respective stars in circular patterns, much like the planets of our solar system.

These 74 exoplanets, which orbit 28 stars, are about the size of Earth, and their circular trajectories stand in stark contrast to those of more massive exoplanets, some of which come extremely close to their stars before hurtling far out in highly eccentric, elongated orbits.

“Twenty years ago, we only knew about our solar system, and everything was circular and so everyone expected circular orbits everywhere,” says Vincent Van Eylen, a visiting graduate student in MIT’s Department of Physics. “Then we started finding giant exoplanets, and we found suddenly a whole range of eccentricities, so there was an open question about whether this would also hold for smaller planets. We find that for small planets, circular is probably the norm.”

Ultimately, Van Eylen says that’s good news in the search for life elsewhere. Among other requirements, for a planet to be habitable, it would have to be about the size of Earth — small and compact enough to be made of rock, not gas. If a small planet also maintained a circular orbit, it would be even more hospitable to life, as it would support a stable climate year-round. (In contrast, a planet with a more eccentric orbit might experience dramatic swings in climate as it orbited close in, then far out from its star.)

“If eccentric orbits are common for habitable planets, that would be quite a worry for life, because they would have such a large range of climate properties,” Van Eylen says. “But what we find is, probably we don’t have to worry too much because circular cases are fairly common.”

Star-crossed numbers

In the past, researchers have calculated the orbital eccentricities of large, “gas giant” exoplanets using radial velocity — a technique that measures a star’s movement. As a planet orbits a star, its gravitational force will tug on the star, causing it to move in a pattern that reflects the planet’s orbit. However, the technique is most successful for larger planets, as they exert enough gravitational pull to influence their stars.

Researchers commonly find smaller planets by using a transit-detecting method, in which they study the light given off by a star, in search of dips in starlight that signify when a planet crosses, or “transits,” in front of that star, momentarily diminishing its light. Ordinarily, this method only illuminates a planet’s existence, not its orbit. But Van Eylen and his colleague Simon Albrecht, of Aarhus University, devised a way to glean orbital information from stellar transit data.

They first reasoned that if they knew the mass and radius of a planet’s star, they could calculate how long a planet would take to orbit that star, if its orbit were circular. The mass and radius of a star determines its gravitational pull, which in turn influences how fast a planet travels around the star.

By calculating a planet’s orbital velocity in a circular orbit, they could then estimate a transit’s duration — how long a planet would take to cross in front of a star. If the calculated transit matched an actual transit, the researchers reasoned that the planet’s orbit must be circular. If the transit were longer or shorter, the orbit must be more elongated, or eccentric.

Not so eccentric

To obtain actual transit data, the team looked through data collected over the past four years by NASA’s Kepler telescope — a space observatory that surveys a slice of the sky in search of habitable planets. The telescope has monitored the brightness of over 145,000 stars, only a fraction of which have been characterized in any detail.

The team chose to concentrate on 28 stars for which mass and radius have previously been measured, using asteroseismology — a technique that measures stellar pulsations, which reflect a star’s mass and radius.

These 28 stars host multiplanet systems — 74 exoplanets in all. The researchers obtained Kepler data for each exoplanet, looking not only for the occurrence of transits, but also their duration. Given the mass and radius of the host stars, the team calculated each planet’s transit duration if its orbit were circular, then compared the estimated transit durations with actual transit durations from Kepler data.

Across the board, Van Eylen and Albrecht found the calculated and actual transit durations matched, suggesting that all 74 exoplanets maintain circular, not eccentric, orbits.

“We found that most of them matched pretty closely, which means they’re pretty close to being circular,” Van Eylen says. “We are very certain that if very high eccentricities were common, we would’ve seen that, which we don’t.”

Van Eylen says the orbital results for these smaller planets may eventually help to explain why larger planets have more extreme orbits.

“We want to understand why some exoplanets have extremely eccentric orbits, while in other cases, such as the solar system, planets orbit mostly circularly,” Van Eylen says. “This is one of the first times we’ve reliably measured the eccentricities of small planets, and it’s exciting to see they are different from the giant planets, but similar to the solar system.”

This research was funded in part by the European Research Council.

 

Related links

ARCHIVE: New technique allows analysis of clouds around exoplanets
http://newsoffice.mit.edu/2015/clouds-around-exoplanets-0303

ARCHIVE: New technique measures mass of exoplanets
http://newsoffice.mit.edu/2013/new-technique-measures-mass-of-exoplanets-1219

ARCHIVE: Researchers discover that an exoplanet is Earth-like in mass and size
http://newsoffice.mit.edu/2013/kepler-78b-earth-like-in-mass-and-size-1030

 

Source: MIT News Office

This image shows the sky around the star 51 Pegasi in the northern constellation of Pegasus (The Winged Horse).  In 1995 the first exoplanet to be discovered was detected orbiting this star. Twenty years later this object was also the first exoplanet to be be directly detected spectroscopically in visible light. This image was created from photographic material forming part of the Digitized Sky Survey 2.

Credit:
ESO/Digitized Sky Survey 2

First Exoplanet Visible Light Spectrum

New technique paints promising picture for future


Astronomers using the HARPS planet-hunting machine at ESO’s La Silla Observatory in Chile have made the first-ever direct detection of the spectrum of visible light reflected off an exoplanet. These observations also revealed new properties of this famous object, the first exoplanet ever discovered around a normal star: 51 Pegasi b. The result promises an exciting future for this technique, particularly with the advent of next generation instruments, such as ESPRESSO, on the VLT, and future telescopes, such as the E-ELT.

The exoplanet 51 Pegasi b [1] lies some 50 light-years from Earth in the constellation of Pegasus. It was discovered in 1995 and will forever be remembered as the first confirmed exoplanet to be found orbiting an ordinary star like the Sun [2]. It is also regarded as the archetypal hot Jupiter — a class of planets now known to be relatively commonplace, which are similar in size and mass to Jupiter, but orbit much closer to their parent stars.

Since that landmark discovery, more than 1900 exoplanets in 1200 planetary systems have been confirmed, but, in the year of the twentieth anniversary of its discovery, 51 Pegasi b returns to the ring once more to provide another advance in exoplanet studies.

The team that made this new detection was led by Jorge Martins from the Instituto de Astrofísica e Ciências do Espaço (IA) and the Universidade do Porto, Portugal, who is currently a PhD student at ESO in Chile. They used the HARPS instrument on the ESO 3.6-metre telescope at the La Silla Observatory in Chile.

This image shows the sky around the star 51 Pegasi in the northern constellation of Pegasus (The Winged Horse).  In 1995 the first exoplanet to be discovered was detected orbiting this star. Twenty years later this object was also the first exoplanet to be be directly detected spectroscopically in visible light. This image was created from photographic material forming part of the Digitized Sky Survey 2. Credit: ESO/Digitized Sky Survey 2
This image shows the sky around the star 51 Pegasi in the northern constellation of Pegasus (The Winged Horse). In 1995 the first exoplanet to be discovered was detected orbiting this star. Twenty years later this object was also the first exoplanet to be be directly detected spectroscopically in visible light. This image was created from photographic material forming part of the Digitized Sky Survey 2.
Credit:
ESO/Digitized Sky Survey 2

Currently, the most widely used method to examine an exoplanet’s atmosphere is to observe the host star’s spectrum as it is filtered through the planet’s atmosphere during transit — a technique known as transmission spectroscopy. An alternative approach is to observe the system when the star passes in front of the planet, which primarily provides information about the exoplanet’s temperature.

The new technique does not depend on finding a planetary transit, and so can potentially be used to study many more exoplanets. It allows the planetary spectrum to be directly detected in visible light, which means that different characteristics of the planet that are inaccessible to other techniques can be inferred.

The host star’s spectrum is used as a template to guide a search for a similar signature of light that is expected to be reflected off the planet as it describes its orbit. This is an exceedingly difficult task as planets are incredibly dim in comparison to their dazzling parent stars.

The signal from the planet is also easily swamped by other tiny effects and sources of noise [3]. In the face of such adversity, the success of the technique when applied to the HARPS data collected on 51 Pegasi b provides an extremely valuable proof of concept.

Jorge Martins explains: “This type of detection technique is of great scientific importance, as it allows us to measure the planet’s real mass and orbital inclination, which is essential to more fully understand the system. It also allows us to estimate the planet’s reflectivity, or albedo, which can be used to infer the composition of both the planet’s surface and atmosphere.”

51 Pegasi b was found to have a mass about half that of Jupiter’s and an orbit with an inclination of about nine degrees to the direction to the Earth [4]. The planet also seems to be larger than Jupiter in diameter and to be highly reflective. These are typical properties for a hot Jupiter that is very close to its parent star and exposed to intense starlight.

HARPS was essential to the team’s work, but the fact that the result was obtained using the ESO 3.6-metre telescope, which has a limited range of application with this technique, is exciting news for astronomers. Existing equipment like this will be surpassed by much more advanced instruments on larger telescopes, such as ESO’s Very Large Telescope and the future European Extremely Large Telescope [5].

“We are now eagerly awaiting first light of the ESPRESSO spectrograph on the VLT so that we can do more detailed studies of this and other planetary systems,” concludes Nuno Santos, of the IA and Universidade do Porto, who is a co-author of the new paper.

Notes
[1] Both 51 Pegasi b and its host star 51 Pegasi are among the objects available for public naming in the IAU’s NameExoWorlds contest.

[2] Two earlier planetary objects were detected orbiting in the extreme environment of a pulsar.

[3] The challenge is similar to trying to study the faint glimmer reflected off a tiny insect flying around a distant and brilliant light.

[4] This means that the planet’s orbit is close to being edge on as seen from Earth, although this is not close enough for transits to take place.

[5] ESPRESSO on the VLT, and later even more powerful instruments on much larger telescopes such as the E-ELT, will allow for a significant increase in precision and collecting power, aiding the detection of smaller exoplanets, while providing an increase in detail in the data for planets similar to 51 Pegasi b.

Source: ESO

Star formation in what are now "dead" galaxies sputtered out billions of years ago. ESO’s Very Large Telescope and the NASA/ESA Hubble Space Telescope have revealed that three billion years after the Big Bang, these galaxies still made stars on their outskirts, but no longer in their interiors. The quenching of star formation seems to have started in the cores of the galaxies and then spread to the outer parts.

This diagram illustrates this process. Galaxies in the early Universe appear at the left. The blue regions are where star formation is in progress and the red regions are the "dead" regions where only older redder stars remain and there are no more young blue stars being formed. The resulting giant spheroidal galaxies in the modern Universe appear on the right.

Credit:
ESO

Giant Galaxies Die from the Inside Out

VLT and Hubble observations show that star formation shuts down in the centres of elliptical galaxies first


Astronomers have shown for the first time how star formation in “dead” galaxies sputtered out billions of years ago. ESO’s Very Large Telescope and the NASA/ESA Hubble Space Telescope have revealed that three billion years after the Big Bang, these galaxies still made stars on their outskirts, but no longer in their interiors. The quenching of star formation seems to have started in the cores of the galaxies and then spread to the outer parts. The results will be published in the 17 April 2015 issue of the journal Science.

Star formation in what are now "dead" galaxies sputtered out billions of years ago. ESO’s Very Large Telescope and the NASA/ESA Hubble Space Telescope have revealed that three billion years after the Big Bang, these galaxies still made stars on their outskirts, but no longer in their interiors. The quenching of star formation seems to have started in the cores of the galaxies and then spread to the outer parts. This diagram illustrates this process. Galaxies in the early Universe appear at the left. The blue regions are where star formation is in progress and the red regions are the "dead" regions where only older redder stars remain and there are no more young blue stars being formed. The resulting giant spheroidal galaxies in the modern Universe appear on the right. Credit: ESO
Star formation in what are now “dead” galaxies sputtered out billions of years ago. ESO’s Very Large Telescope and the NASA/ESA Hubble Space Telescope have revealed that three billion years after the Big Bang, these galaxies still made stars on their outskirts, but no longer in their interiors. The quenching of star formation seems to have started in the cores of the galaxies and then spread to the outer parts.
This diagram illustrates this process. Galaxies in the early Universe appear at the left. The blue regions are where star formation is in progress and the red regions are the “dead” regions where only older redder stars remain and there are no more young blue stars being formed. The resulting giant spheroidal galaxies in the modern Universe appear on the right.
Credit:
ESO

A major astrophysical mystery has centred on how massive, quiescent elliptical galaxies, common in the modern Universe, quenched their once furious rates of star formation. Such colossal galaxies, often also called spheroids because of their shape, typically pack in stars ten times as densely in the central regions as in our home galaxy, the Milky Way, and have about ten times its mass.

Astronomers refer to these big galaxies as red and dead as they exhibit an ample abundance of ancient red stars, but lack young blue stars and show no evidence of new star formation. The estimated ages of the red stars suggest that their host galaxies ceased to make new stars about ten billion years ago. This shutdown began right at the peak of star formation in the Universe, when many galaxies were still giving birth to stars at a pace about twenty times faster than nowadays.

“Massive dead spheroids contain about half of all the stars that the Universe has produced during its entire life,” said Sandro Tacchella of ETH Zurich in Switzerland, lead author of the article. “We cannot claim to understand how the Universe evolved and became as we see it today unless we understand how these galaxies come to be.”

Tacchella and colleagues observed a total of 22 galaxies, spanning a range of masses, from an era about three billion years after the Big Bang [1]. The SINFONI instrument on ESO’s Very Large Telescope (VLT) collected light from this sample of galaxies, showing precisely where they were churning out new stars. SINFONI could make these detailed measurements of distant galaxies thanks to its adaptive optics system, which largely cancels out the blurring effects of Earth’s atmosphere.

The researchers also trained the NASA/ESA Hubble Space Telescope on the same set of galaxies, taking advantage of the telescope’s location in space above our planet’s distorting atmosphere. Hubble’s WFC3 camera snapped images in the near-infrared, revealing the spatial distribution of older stars within the actively star-forming galaxies.

“What is amazing is that SINFONI’s adaptive optics system can largely beat down atmospheric effects and gather information on where the new stars are being born, and do so with precisely the same accuracy as Hubble allows for the stellar mass distributions,” commented Marcella Carollo, also of ETH Zurich and co-author of the study.

According to the new data, the most massive galaxies in the sample kept up a steady production of new stars in their peripheries. In their bulging, densely packed centres, however, star formation had already stopped.

“The newly demonstrated inside-out nature of star formation shutdown in massive galaxies should shed light on the underlying mechanisms involved, which astronomers have long debated,” says Alvio Renzini, Padova Observatory, of the Italian National Institute of Astrophysics.

A leading theory is that star-making materials are scattered by torrents of energy released by a galaxy’s central supermassive black hole as it sloppily devours matter. Another idea is that fresh gas stops flowing into a galaxy, starving it of fuel for new stars and transforming it into a red and dead spheroid.

“There are many different theoretical suggestions for the physical mechanisms that led to the death of the massive spheroids,” said co-author Natascha Förster Schreiber, at the Max-Planck-Institut für extraterrestrische Physik in Garching, Germany. “Discovering that the quenching of star formation started from the centres and marched its way outwards is a very important step towards understanding how the Universe came to look like it does now.”

Notes
[1] The Universe’s age is about 13.8 billion years, so the galaxies studied by Tacchella and colleagues are generally seen as they were more than 10 billion years ago.

Source: ESO


ALMA Reveals Intense Magnetic Field Close to Supermassive Black Hole

Illuminating the mysterious mechanisms at play at the edge of the event horizon


This artist’s impression shows the surroundings of a supermassive black hole, typical of that found at the heart of many galaxies. The black hole itself is surrounded by a brilliant accretion disc of very hot, infalling material and, further out, a dusty torus. There are also often high-speed jets of material ejected at the black hole’s poles that can extend huge distances into space. Observations with ALMA have detected a very strong magnetic field close to the black hole at the base of the jets and this is probably involved in jet production and collimation. Credit: ESO/L. Calçada
This artist’s impression shows the surroundings of a supermassive black hole, typical of that found at the heart of many galaxies. The black hole itself is surrounded by a brilliant accretion disc of very hot, infalling material and, further out, a dusty torus. There are also often high-speed jets of material ejected at the black hole’s poles that can extend huge distances into space. Observations with ALMA have detected a very strong magnetic field close to the black hole at the base of the jets and this is probably involved in jet production and collimation.
Credit:
ESO/L. Calçada

The Atacama Large Millimeter/submillimeter Array (ALMA) has revealed an extremely powerful magnetic field, beyond anything previously detected in the core of a galaxy, very close to the event horizon of a supermassive black hole. This new observation helps astronomers to understand the structure and formation of these massive inhabitants of the centres of galaxies, and the twin high-speed jets of plasma they frequently eject from their poles. The results appear in the 17 April 2015 issue of the journal Science.

Supermassive black holes, often with masses billions of times that of the Sun, are located at the heart of almost all galaxies in the Universe. These black holes can accrete huge amounts of matter in the form of a surrounding disc. While most of this matter is fed into the black hole, some can escape moments before capture and be flung out into space at close to the speed of light as part of a jet of plasma. How this happens is not well understood, although it is thought that strong magnetic fields, acting very close to the event horizon, play a crucial part in this process, helping the matter to escape from the gaping jaws of darkness.

Up to now only weak magnetic fields far from black holes — several light-years away — had been probed [1]. In this study, however, astronomers from Chalmers University of Technology and Onsala Space Observatory in Sweden have now used ALMA to detect signals directly related to a strong magnetic field very close to the event horizon of the supermassive black hole in a distant galaxy named PKS 1830-211. This magnetic field is located precisely at the place where matter is suddenly boosted away from the black hole in the form of a jet.

The team measured the strength of the magnetic field by studying the way in which light was polarised, as it moved away from the black hole.

“Polarisation is an important property of light and is much used in daily life, for example in sun glasses or 3D glasses at the cinema,” says Ivan Marti-Vidal, lead author of this work. “When produced naturally, polarisation can be used to measure magnetic fields, since light changes its polarisation when it travels through a magnetised medium. In this case, the light that we detected with ALMA had been travelling through material very close to the black hole, a place full of highly magnetised plasma.”

The astronomers applied a new analysis technique that they had developed to the ALMA data and found that the direction of polarisation of the radiation coming from the centre of PKS 1830-211 had rotated [2]. These are the shortest wavelengths ever used in this kind of study, which allow the regions very close to the central black hole to be probed [3].

“We have found clear signals of polarisation rotation that are hundreds of times higher than the highest ever found in the Universe,” says Sebastien Muller, co-author of the paper. “Our discovery is a giant leap in terms of observing frequency, thanks to the use of ALMA, and in terms of distance to the black hole where the magnetic field has been probed — of the order of only a few light-days from the event horizon. These results, and future studies, will help us understand what is really going on in the immediate vicinity of supermassive black holes.”

Notes
[1] Much weaker magnetic fields have been detected in the vicinity of the relatively inactive supermassive black hole at the centre of the Milky Way. Recent observations have also revealed weak magnetic fields in the active galaxy NGC 1275, which were detected at millimetre wavelengths.

[2] Magnetic fields introduce Faraday rotation, which makes the polarisation rotate in different ways at different wavelengths. The way in which this rotation depends on the wavelength tells us about the magnetic field in the region.

[3] The ALMA observations were at an effective wavelength of about 0.3 millimetres, earlier investigations were at much longer radio wavelengths. Only light of millimetre wavelengths can escape from the region very close to the black hole, longer wavelength radiation is absorbed.

Source: ESO


First Signs of Self-interacting Dark Matter?

Dark matter may not be completely dark after all


Based on our current scientific understanding of the universe and various surveys like the Cosmic Microwave Background observations by Planck or WMAP, we still only know about 4-5% of the visible or baryonic matter. Rest of the 96-94% is still a mystery. This huge unknown portion of the dark universe is known to be comprised of the dark energy (the source of accelerating expansion of the universe)  and dark matter (the extra un-explained mass of the galaxies). Despite having indirect signatures suggesting their presence, we still are not able to observe these phenomena.

For the first time dark matter may have been observed interacting with other dark matter in a way other than through the force of gravity. Observations of colliding galaxies made with ESO’s Very Large Telescope and the NASA/ESA Hubble Space Telescope have picked up the first intriguing hints about the nature of this mysterious component of the Universe.

This image from the NASA/ESA Hubble Space Telescope shows the rich galaxy cluster Abell 3827. The strange pale blue structures surrounding the central galaxies are gravitationally lensed views of a much more distant galaxy behind the cluster. The distribution of dark matter in the cluster is shown with blue contour lines. The dark matter clump for the galaxy at the left is significantly displaced from the position of the galaxy itself, possibly implying dark matter-dark matter interactions of an unknown nature are occuring. Credit: ESO/R. Massey
This image from the NASA/ESA Hubble Space Telescope shows the rich galaxy cluster Abell 3827. The strange pale blue structures surrounding the central galaxies are gravitationally lensed views of a much more distant galaxy behind the cluster.
The distribution of dark matter in the cluster is shown with blue contour lines. The dark matter clump for the galaxy at the left is significantly displaced from the position of the galaxy itself, possibly implying dark matter-dark matter interactions of an unknown nature are occuring.
Credit:
ESO/R. Massey

Using the MUSE instrument on ESO’s VLT in Chile, along with images from Hubble in orbit, a team of astronomers studied the simultaneous collision of four galaxies in the galaxy cluster Abell 3827. The team could trace out where the mass lies within the system and compare the distribution of the dark matter with the positions of the luminous galaxies.

Although dark matter cannot be seen, the team could deduce its location using a technique called gravitational lensing. The collision happened to take place directly in front of a much more distant, unrelated source. The mass of dark matter around the colliding galaxies severely distorted spacetime, deviating the path of light rays coming from the distant background galaxy — and distorting its image into characteristic arc shapes.

Our current understanding is that all galaxies exist inside clumps of dark matter. Without the constraining effect of dark matter’s gravity, galaxies like the Milky Way would fling themselves apart as they rotate. In order to prevent this, 85 percent of the Universe’s mass [1] must exist as dark matter, and yet its true nature remains a mystery.

In this study, the researchers observed the four colliding galaxies and found that one dark matter clump appeared to be lagging behind the galaxy it surrounds. The dark matter is currently 5000 light-years (50 000 million million kilometres) behind the galaxy — it would take NASA’s Voyager spacecraft 90 million years to travel that far.

A lag between dark matter and its associated galaxy is predicted during collisions if dark matter interacts with itself, even very slightly, through forces other than gravity [2]. Dark matter has never before been observed interacting in any way other than through the force of gravity.

Lead author Richard Massey at Durham University, explains: “We used to think that dark matter just sits around, minding its own business, except for its gravitational pull. But if dark matter were being slowed down during this collision, it could be the first evidence for rich physics in the dark sector — the hidden Universe all around us.”

The researchers note that more investigation will be needed into other effects that could also produce a lag. Similar observations of more galaxies, and computer simulations of galaxy collisions will need to be made.

Team member Liliya Williams of the University of Minnesota adds: “We know that dark matter exists because of the way that it interacts gravitationally, helping to shape the Universe, but we still know embarrassingly little about what dark matter actually is. Our observation suggests that dark matter might interact with forces other than gravity, meaning we could rule out some key theories about what dark matter might be.”

This result follows on from a recent result from the team which observed 72 collisions between galaxy clusters [3] and found that dark matter interacts very little with itself. The new work however concerns the motion of individual galaxies, rather than clusters of galaxies. Researchers say that the collision between these galaxies could have lasted longer than the collisions observed in the previous study — allowing the effects of even a tiny frictional force to build up over time and create a measurable lag [4].

Taken together, the two results bracket the behaviour of dark matter for the first time. Dark matter interacts more than this, but less than that. Massey added: “We are finally homing in on dark matter from above and below — squeezing our knowledge from two directions.”

Notes
[1] Astronomers have found that the total mass/energy content of the Universe is split in the proportions 68% dark energy, 27% dark matter and 5% “normal” matter. So the 85% figure relates to the fraction of “matter” that is dark.

[2] Computer simulations show that the extra friction from the collision would make the dark matter slow down. The nature of that interaction is unknown; it could be caused by well-known effects or some exotic unknown force. All that can be said at this point is that it is not gravity.

All four galaxies might have been separated from their dark matter. But we happen to have a very good measurement from only one galaxy, because it is by chance aligned so well with the background, gravitationally lensed object. With the other three galaxies, the lensed images are further away, so the constraints on the location of their dark matter too loose to draw statistically significant conclusions.

[3] Galaxy clusters contain up to a thousand individual galaxies.

[4] The main uncertainty in the result is the timespan for the collision: the friction that slowed the dark matter could have been a very weak force acting over about a billion years, or a relatively stronger force acting for “only” 100 million years.

Source: ESO

This chart of the position of a nova (marked in red) that appeared in the year 1670 was recorded by the famous astronomer Hevelius and was published by the Royal Society in England in their journal Philosophical Transactions.

New observations made with APEX and other telescopes have now revealed that the star that European astronomers saw was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later.

Credit:
Royal Society

Colliding Stars Explain Enigmatic Seventeenth Century Explosion

APEX observations help unravel mystery of Nova Vulpeculae 1670


New observations made with APEX and other telescopes reveal that the star that European astronomers saw appear in the sky in 1670 was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later. The results appear online in the journal Nature on 23 March 2015.

This chart of the position of a nova (marked in red) that appeared in the year 1670 was recorded by the famous astronomer Hevelius and was published by the Royal Society in England in their journal Philosophical Transactions. New observations made with APEX and other telescopes have now revealed that the star that European astronomers saw was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later. Credit: Royal Society
This chart of the position of a nova (marked in red) that appeared in the year 1670 was recorded by the famous astronomer Hevelius and was published by the Royal Society in England in their journal Philosophical Transactions.
New observations made with APEX and other telescopes have now revealed that the star that European astronomers saw was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later.
Credit:
Royal Society

Some of seventeenth century’s greatest astronomers, including Hevelius — the father of lunar cartography — and Cassini, carefully documented the appearance of a new star in the skies in 1670. Hevelius described it as nova sub capite Cygni — a new star below the head of the Swan — but astronomers now know it by the name Nova Vulpeculae 1670 [1]. Historical accounts of novae are rare and of great interest to modern astronomers. Nova Vul 1670 is claimed to be both the oldest recorded nova and the faintest nova when later recovered.

The lead author of the new study, Tomasz Kamiński (ESO and the Max Planck Institute for Radio Astronomy, Bonn, Germany) explains: “For many years this object was thought to be a nova, but the more it was studied the less it looked like an ordinary nova — or indeed any other kind of exploding star.”

When it first appeared, Nova Vul 1670 was easily visible with the naked eye and varied in brightness over the course of two years. It then disappeared and reappeared twice before vanishing for good. Although well documented for its time, the intrepid astronomers of the day lacked the equipment needed to solve the riddle of the apparent nova’s peculiar performance.

During the twentieth century, astronomers came to understand that most novae could be explained by the runaway explosive behaviour of close binary stars. But Nova Vul 1670 did not fit this model well at all and remained a mystery.

Even with ever-increasing telescopic power, the event was believed for a long time to have left no trace, and it was not until the 1980s that a team of astronomers detected a faint nebula surrounding the suspected location of what was left of the star. While these observations offered a tantalising link to the sighting of 1670, they failed to shed any new light on the true nature of the event witnessed over the skies of Europe over three hundred years ago.

This picture shows the remains of the new star that was seen in the year 1670. It was created from a combination of visible-light images from the Gemini telescope (blue), a submillimetre map showing the dust from the SMA (green) and finally a map of the molecular emission from APEX and the SMA (red). The star that European astronomers saw in 1670 was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later. Credit: ESO/T. Kamiński
This picture shows the remains of the new star that was seen in the year 1670. It was created from a combination of visible-light images from the Gemini telescope (blue), a submillimetre map showing the dust from the SMA (green) and finally a map of the molecular emission from APEX and the SMA (red).
The star that European astronomers saw in 1670 was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later.
Credit:
ESO/T. Kamiński

 

Tomasz Kamiński continues the story: “We have now probed the area with submillimetre and radio wavelengths. We have found that the surroundings of the remnant are bathed in a cool gas rich in molecules, with a very unusual chemical composition.”

As well as APEX, the team also used the Submillimeter Array (SMA) and the Effelsberg radio telescope to discover the chemical composition and measure the ratios of different isotopes in the gas. Together, this created an extremely detailed account of the makeup of the area, which allowed an evaluation of where this material might have come from.

What the team discovered was that the mass of the cool material was too great to be the product of a nova explosion, and in addition the isotope ratios the team measured around Nova Vul 1670 were different to those expected from a nova. But if it wasn’t a nova, then what was it?

The answer is a spectacular collision between two stars, more brilliant than a nova, but less so than a supernova, which produces something called a red transient. These are a very rare events in which stars explode due to a merger with another star, spewing material from the stellar interiors into space, eventually leaving behind only a faint remnant embedded in a cool environment, rich in molecules and dust. This newly recognised class of eruptive stars fits the profile of Nova Vul 1670 almost exactly.

Co-author Karl Menten (Max Planck Institute for Radio Astronomy, Bonn, Germany) concludes: “This kind of discovery is the most fun: something that is completely unexpected!”

Notes
[1] This object lies within the boundaries of the modern constellation of Vulpecula (The Fox), just across the border from Cygnus (The Swan). It is also often referred to as Nova Vul 1670 and CK Vulpeculae, its designation as a variable star.

Source: ESO News

 

This artist’s impression shows how Mars may have looked about four billion years ago. The young planet Mars would have had enough water to cover its entire surface in a liquid layer about 140 metres deep, but it is more likely that the liquid would have pooled to form an ocean occupying almost half of Mars’s northern hemisphere, and in some regions reaching depths greater than 1.6 kilometres.

Credit:
ESO/M. Kornmesser

Mars, the Red Planet once had more water than Earth’s Arctic Ocean

Researchers, from ESO, NASA and Keck, who are studying Mars’ atmosphere have provided some exciting results regarding the history of water on the red planet.


 

A primitive ocean on Mars held more water than Earth’s Arctic Ocean, and covered a greater portion of the planet’s surface than the Atlantic Ocean does on Earth, according to new results published today. An international team of scientists used ESO’s Very Large Telescope, along with instruments at the W. M. Keck Observatory and the NASA Infrared Telescope Facility, to monitor the atmosphere of the planet and map out the properties of the water in different parts of Mars’s atmosphere over a six-year period. These new maps are the first of their kind. The results appear online in the journal Science today.

About four billion years ago, the young planet would have had enough water to cover its entire surface in a liquid layer about 140 metres deep, but it is more likely that the liquid would have pooled to form an ocean occupying almost half of Mars’s northern hemisphere, and in some regions reaching depths greater than 1.6 kilometres.

Our study provides a solid estimate of how much water Mars once had, by determining how much water was lost to space,” said Geronimo Villanueva, a scientist working at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, USA, and lead author of the new paper. “With this work, we can better understand the history of water on Mars.

This artist’s impression shows how Mars may have looked about four billion years ago. The young planet Mars would have had enough water to cover its entire surface in a liquid layer about 140 metres deep, but it is more likely that the liquid would have pooled to form an ocean occupying almost half of Mars’s northern hemisphere, and in some regions reaching depths greater than 1.6 kilometres. Credit: ESO/M. Kornmesser
This artist’s impression shows how Mars may have looked about four billion years ago. The young planet Mars would have had enough water to cover its entire surface in a liquid layer about 140 metres deep, but it is more likely that the liquid would have pooled to form an ocean occupying almost half of Mars’s northern hemisphere, and in some regions reaching depths greater than 1.6 kilometres.
Credit:
ESO/M. Kornmesser

The new estimate is based on detailed observations of two slightly different forms of water in Mars’s atmosphere. One is the familiar form of water, made with two hydrogen atoms and one oxygen, H2O. The other is HDO, or semi-heavy water, a naturally occurring variation in which one hydrogen atom is replaced by a heavier form, called deuterium.

As the deuterated form is heavier than normal water, it is less easily lost into space through evaporation. So, the greater the water loss from the planet, the greater the ratio of HDO to H2O in the water that remains [1].

The researchers distinguished the chemical signatures of the two types of water using ESO’s Very Large Telescope in Chile, along with instruments at the W. M. Keck Observatory and the NASA Infrared Telescope Facility in Hawaii [2]. By comparing the ratio of HDO to H2O, scientists can measure by how much the fraction of HDO has increased and thus determine how much water has escaped into space. This in turn allows the amount of water on Mars at earlier times to be estimated.

In the study, the team mapped the distribution of H2O and HDO repeatedly over nearly six Earth years — equal to about three Mars years — producing global snapshots of each, as well as their ratio. The maps reveal seasonal changes and microclimates, even though modern Mars is essentially a desert.

Ulli Kaeufl of ESO, who was responsible for building one of the instruments used in this study and is a co-author of the new paper, adds: “I am again overwhelmed by how much power there is in remote sensing on other planets using astronomical telescopes: we found an ancient ocean more than 100 million kilometres away!” 

The team was especially interested in regions near the north and south poles, because the polar ice caps are the planet’s largest known reservoir of water. The water stored there is thought to document the evolution of Mars’s water from the wet Noachian period, which ended about 3.7 billion years ago, to the present.

The new results show that atmospheric water in the near-polar region was enriched in HDO by a factor of seven relative to Earth’s ocean water, implying that water in Mars’s permanent ice caps is enriched eight-fold. Mars must have lost a volume of water 6.5 times larger than the present polar caps to provide such a high level of enrichment. The volume of Mars’s early ocean must have been at least 20 million cubic kilometres.

Based on the surface of Mars today, a likely location for this water would be the Northern Plains, which have long been considered a good candidate because of their low-lying ground. An ancient ocean there would have covered 19% of the planet’s surface — by comparison, the Atlantic Ocean occupies 17% of the Earth’s surface.

With Mars losing that much water, the planet was very likely wet for a longer period of time than previously thought, suggesting the planet might have been habitable for longer,” said Michael Mumma, a senior scientist at Goddard and the second author on the paper.

It is possible that Mars once had even more water, some of which may have been deposited below the surface. Because the new maps reveal microclimates and changes in the atmospheric water content over time, they may also prove to be useful in the continuing search for underground water.

Notes

[1] In oceans on Earth there are about 3200 molecules of H2O for each HDO molecule.

[2] Although probes on the Martian surface and orbiting the planet can provide much more detailed in situmeasurements, they are not suitable for monitoring the properties of the whole Martian atmosphere. This is best done using infrared spectrographs on large telescopes back on Earth.

Source: ESO


 

Polarisation of the Cosmic Microwave Background

Credit: ESA/PLANCK

PLANCK Reveals First Starts Were Formed Much Later Than Previously Thought

New maps from ESA’s Planck satellite uncover the ‘polarised’ light from the early Universe across the entire sky, revealing that the first stars formed much later than previously thought.

The history of our Universe is a 13.8 billion-year tale that scientists endeavour to read by studying the planets, asteroids, comets and other objects in our Solar System, and gathering light emitted by distant stars, galaxies and the matter spread between them.

Polarisation of the Cosmic Microwave Background Credit: ESA/PLANCK
Polarisation of the Cosmic Microwave Background
Credit: ESA/PLANCK

A major source of information used to piece together this story is the Cosmic Microwave Background, or CMB, the fossil light resulting from a time when the Universe was hot and dense, only 380 000 years after the Big Bang.

Thanks to the expansion of the Universe, we see this light today covering the whole sky at microwave wavelengths.

Between 2009 and 2013, Planck surveyed the sky to study this ancient light in unprecedented detail. Tiny differences in the background’s temperature trace regions of slightly different density in the early cosmos, representing the seeds of all future structure, the stars and galaxies of today.

Scientists from the Planck collaboration have published the results from the analysis of these data in a large number of scientific papers over the past two years, confirming the standard cosmological picture of our Universe with ever greater accuracy.

History of the Universe Credit:ESA
History of the Universe
Credit:ESA

“But there is more: the CMB carries additional clues about our cosmic history that are encoded in its ‘polarisation’,” explains Jan Tauber, ESA’s Planck project scientist.

“Planck has measured this signal for the first time at high resolution over the entire sky, producing the unique maps released today.”

Light is polarised when it vibrates in a preferred direction, something that may arise as a result of photons – the particles of light – bouncing off other particles. This is exactly what happened when the CMB originated in the early Universe.

Initially, photons were trapped in a hot, dense soup of particles that, by the time the Universe was a few seconds old, consisted mainly of electrons, protons and neutrinos. Owing to the high density, electrons and photons collided with one another so frequently that light could not travel any significant distant before bumping into another electron, making the early Universe extremely ‘foggy’.

Slowly but surely, as the cosmos expanded and cooled, photons and the other particles grew farther apart, and collisions became less frequent.

This had two consequences: electrons and protons could finally combine and form neutral atoms without them being torn apart again by an incoming photon, and photons had enough room to travel, being no longer trapped in the cosmic fog.

Once freed from the fog, the light was set on its cosmic journey that would take it all the way to the present day, where telescopes like Planck detect it as the CMB. But the light also retains a memory of its last encounter with the electrons, captured in its polarisation.

“The polarisation of the CMB also shows minuscule fluctuations from one place to another across the sky: like the temperature fluctuations, these reflect the state of the cosmos at the time when light and matter parted company,” says François Bouchet of the Institut d’Astrophysique de Paris, France.

“This provides a powerful tool to estimate in a new and independent way parameters such as the age of the Universe, its rate of expansion and its essential composition of normal matter, dark matter and dark energy.”

Planck’s polarisation data confirm the details of the standard cosmological picture determined from its measurement of the CMB temperature fluctuations, but add an important new answer to a fundamental question: when were the first stars born?

“After the CMB was released, the Universe was still very different from the one we live in today, and it took a long time until the first stars were able to form,” explains Marco Bersanelli of Università degli Studi di Milano, Italy.

“Planck’s observations of the CMB polarisation now tell us that these ‘Dark Ages’ ended some 550 million years after the Big Bang – more than 100 million years later than previously thought.

“While these 100 million years may seem negligible compared to the Universe’s age of almost 14 billion years, they make a significant difference when it comes to the formation of the first stars.”

The Dark Ages ended as the first stars began to shine. And as their light interacted with gas in the Universe, more and more of the atoms were turned back into their constituent particles: electrons and protons.

This key phase in the history of the cosmos is known as the ‘epoch of reionisation’.

The newly liberated electrons were once again able to collide with the light from the CMB, albeit much less frequently now that the Universe had significantly expanded. Nevertheless, just as they had 380 000 years after the Big Bang, these encounters between electrons and photons left a tell-tale imprint on the polarisation of the CMB.

“From our measurements of the most distant galaxies and quasars, we know that the process of reionisation was complete by the time that the Universe was about 900 million years old,” says George Efstathiou of the University of Cambridge, UK.

“But, at the moment, it is only with the CMB data that we can learn when this process began.”

Planck’s new results are critical, because previous studies of the CMB polarisation seemed to point towards an earlier dawn of the first stars, placing the beginning of reionisation about 450 million years after the Big Bang.

This posed a problem. Very deep images of the sky from the NASA–ESA Hubble Space Telescope have provided a census of the earliest known galaxies in the Universe, which started forming perhaps 300–400 million years after the Big Bang.

However, these would not have been powerful enough to succeed at ending the Dark Ages within 450 million years.

“In that case, we would have needed additional, more exotic sources of energy to explain the history of reionisation,” says Professor Efstathiou.

The new evidence from Planck significantly reduces the problem, indicating that reionisation started later than previously believed, and that the earliest stars and galaxies alone might have been enough to drive it.

This later end of the Dark Ages also implies that it might be easier to detect the very first generation of galaxies with the next generation of observatories, including the James Webb Space Telescope.

But the first stars are definitely not the limit. With the new Planck data released today, scientists are also studying the polarisation of foreground emission from gas and dust in the Milky Way to analyse the structure of the Galactic magnetic field.

The data have also enabled new important insights into the early cosmos and its components, including the intriguing dark matter and the elusive neutrinos, as described in papers also released today.

The Planck data have delved into the even earlier history of the cosmos, all the way to inflation – the brief era of accelerated expansion that the Universe underwent when it was a tiny fraction of a second old. As the ultimate probe of this epoch, astronomers are looking for a signature of gravitational waves triggered by inflation and later imprinted on the polarisation of the CMB.

No direct detection of this signal has yet been achieved, as reported last week. However, when combining the newest all-sky Planck data with those latest results, the limits on the amount of primordial gravitational waves are pushed even further down to achieve the best upper limits yet.

“These are only a few highlights from the scrutiny of Planck’s observations of the CMB polarisation, which is revealing the sky and the Universe in a brand new way,” says Jan Tauber.

“This is an incredibly rich data set and the harvest of discoveries has just begun.”

A series of scientific papers describing the new results was published on 5 February and it can be downloaded here.

The new results from Planck are based on the complete surveys of the entire sky, performed between 2009 and 2013. New data, including temperature maps of the CMB at all nine frequencies observed by Planck and polarisation maps at four frequencies (30, 44, 70 and 353 GHz), are also released today.

The three principal scientific leaders of the Planck mission, Nazzareno Mandolesi, Jean-Loup Puget and Jan Tauber, were recently awarded the 2015 EPS Edison Volta Prize for “directing the development of the Planck payload and the analysis of its data, resulting in the refinement of our knowledge of the temperature fluctuations in the Cosmic Microwave Background as a vastly improved tool for doing precision cosmology at unprecedented levels of accuracy, and consolidating our understanding of the very early universe.

More about Planck

Launched in 2009, Planck was designed to map the sky in nine frequencies using two state-of-the-art instruments: the Low Frequency Instrument (LFI), which includes three frequency bands in the range 30–70 GHz, and the High Frequency Instrument (HFI), which includes six frequency bands in the range 100–857 GHz.

HFI completed its survey in January 2012, while LFI continued to make science observations until 3 October 2013, before being switched off on 19 October 2013. Seven of Planck’s nine frequency channels were equipped with polarisation-sensitive detectors.

The Planck Scientific Collaboration consists of all the scientists who have contributed to the development of the mission, and who participate in the scientific exploitation of the data during the proprietary period.

These scientists are members of one or more of four consortia: the LFI Consortium, the HFI Consortium, the DK-Planck Consortium, and ESA’s Planck Science Office. The two European-led Planck Data Processing Centres are located in Paris, France and Trieste, Italy.

The LFI consortium is led by N. Mandolesi, Università degli Studi di Ferrara, Italy (deputy PI: M. Bersanelli, Università degli Studi di Milano, Italy), and was responsible for the development and operation of LFI. The HFI consortium is led by J.L. Puget, Institut d’Astrophysique Spatiale in Orsay (CNRS/Université Paris-Sud), France (deputy PI: F. Bouchet, Institut d’Astrophysique de Paris (CNRS/UPMC), France), and was responsible for the development and operation of HFI.

Source: ESA

The Mouth of the Beast

VLT images cometary globule CG4


Like the gaping mouth of a gigantic celestial creature, the cometary globule CG4 glows menacingly in this new image from ESO’s Very Large Telescope. Although it appears to be big and bright in this picture, this is actually a faint nebula, which makes it very hard for amateur astronomers to spot. The exact nature of CG4 remains a mystery.

Like the gaping mouth of a gigantic celestial creature, the cometary globule CG4 glows menacingly in this image from ESO’s Very Large Telescope. Although it looks huge and bright in this image it is actually a faint nebula and not easy to observe. The exact nature of CG4 remains a mystery. Credit: ESO
Like the gaping mouth of a gigantic celestial creature, the cometary globule CG4 glows menacingly in this image from ESO’s Very Large Telescope. Although it looks huge and bright in this image it is actually a faint nebula and not easy to observe. The exact nature of CG4 remains a mystery.
Credit:
ESO

In 1976 several elongated comet-like objects were discovered on pictures taken with the UK Schmidt Telescope in Australia. Because of their appearance, they became known as cometary globules even though they have nothing in common with comets. They were all located in a huge patch of glowing gas called the Gum Nebula. They had dense, dark, dusty heads and long, faint tails, which were generally pointing away from the Vela supernova remnant located at the centre of the Gum Nebula. Although these objects are relatively close by, it took astronomers a long time to find them as they glow very dimly and are therefore hard to detect.

The object shown in this new picture, CG4, which is also sometimes referred to as God’s Hand, is one of these cometary globules. It is located about 1300 light-years from Earth in the constellation of Puppis (The Poop, or Stern).

The head of CG4, which is the part visible on this image and resembles the head of the gigantic beast, has a diameter of 1.5 light-years. The tail of the globule — which extends downwards and is not visible in the image — is about eight light-years long. By astronomical standards this makes it a comparatively small cloud.

The relatively small size is a general feature of cometary globules. All of the cometary globules found so far are isolated, relatively small clouds of neutral gas and dust within the Milky Way, which are surrounded by hot ionised material.

The head part of CG4 is a thick cloud of gas and dust, which is only visible because it is illuminated by the light from nearby stars. The radiation emitted by these stars is gradually destroying the head of the globule and eroding away the tiny particles that scatter the starlight. However, the dusty cloud of CG4 still contains enough gas to make several Sun-sized stars and indeed, CG4 is actively forming new stars, perhaps triggered as radiation from the stars powering the Gum Nebula reached CG4.

Why CG4 and other cometary globules have their distinct form is still a matter of debate among astronomers and two theories have developed. Cometary globules, and therefore also CG4, could originally have been spherical nebulae, which were disrupted and acquired their new, unusual form because of the effects of a nearby supernova explosion. Other astronomers suggest, that cometary globules are shaped by stellar winds and ionising radiation from hot, massiveOB stars. These effects could first lead to the bizarrely (but appropriately!) named formations known as elephant trunksand then eventually cometary globules.

To find out more, astronomers need to find out the mass, density, temperature, and velocities of the material in the globules. These can be determined by the measurements of molecular spectral lines which are most easily accessible at millimetre wavelengths — wavelengths at which telescopes like the Atacama Large Millimeter/submillimeter Array (ALMA) operate.

This picture comes from the ESO Cosmic Gems programme, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.

Source: ESO

The enormous structure, dubbed the Fermi Bubbles, was discovered five years ago as a gamma-ray glow on the sky in the direction of the galactic center. The balloon-like features have since been observed in X-rays and radio waves. But astronomers needed NASA's Hubble Space Telescope to measure for the first time the velocity and composition of the mystery lobes. 

Credit: Hubble Site

Hubble Discovers that Milky Way Core Drives Wind at 2 Million Miles Per Hour

At a time when our earliest human ancestors had recently mastered walking upright, the heart of our Milky Way galaxy underwent a titanic eruption, driving gases and other material outward at 2 million miles per hour.

Now, at least 2 million years later, astronomers are witnessing the aftermath of the explosion: billowing clouds of gas towering about 30,000 light-years above and below the plane of our galaxy.

The enormous structure was discovered five years ago as a gamma-ray glow on the sky in the direction of the galactic center. The balloon-like features have since been observed in X-rays and radio waves. But astronomers needed NASA’s Hubble Space Telescope to measure for the first time the velocity and composition of the mystery lobes. They now seek to calculate the mass of the material being blown out of our galaxy, which could lead them to determine the outburst’s cause from several competing scenarios.

Astronomers have proposed two possible origins for the bipolar lobes: a firestorm of star birth at the Milky Way’s center or the eruption of its supermassive black hole. Although astronomers have seen gaseous winds, composed of streams of charged particles, emanating from the cores of other galaxies, they are getting a unique, close-up view of our galaxy’s own fireworks.

“When you look at the centers of other galaxies, the outflows appear much smaller because the galaxies are farther away,” said Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland, lead researcher of the study. “But the outflowing clouds we’re seeing are only 25,000 light-years away in our galaxy. We have a front-row seat. We can study the details of these structures. We can look at how big the bubbles are and can measure how much of the sky they are covering.”

Fox’s results will be published in The Astrophysical Journal Letters and will be presented at the American Astronomical Society meeting in Seattle, Washington.

The giant lobes, dubbed Fermi Bubbles, initially were spotted using NASA’s Fermi Gamma-ray Space Telescope. The detection of high-energy gamma rays suggested that a violent event in the galaxy’s core aggressively launched energized gas into space. To provide more information about the outflows, Fox used Hubble’s Cosmic Origins Spectrograph (COS) to probe the ultraviolet light from a distant quasar that lies behind the base of the northern bubble. Imprinted on that light as it travels through the lobe is information about the velocity, composition, and temperature of the expanding gas inside the bubble, which only COS can provide.

The enormous structure, dubbed the Fermi Bubbles, was discovered five years ago as a gamma-ray glow on the sky in the direction of the galactic center. The balloon-like features have since been observed in X-rays and radio waves. But astronomers needed NASA's Hubble Space Telescope to measure for the first time the velocity and composition of the mystery lobes.  Credit: Hubble Site
The enormous structure, dubbed the Fermi Bubbles, was discovered five years ago as a gamma-ray glow on the sky in the direction of the galactic center. The balloon-like features have since been observed in X-rays and radio waves. But astronomers needed NASA’s Hubble Space Telescope to measure for the first time the velocity and composition of the mystery lobes.
Credit: Hubble Site

Fox’s team was able to measure that the gas on the near side of the bubble is moving toward Earth and the gas on the far side is travelling away. COS spectra show that the gas is rushing from the galactic center at roughly 2 million miles an hour (3 million kilometers an hour).

“This is exactly the signature we knew we would get if this was a bipolar outflow,” explained Rongmon Bordoloi of the Space Telescope Science Institute, a co-author on the science paper. “This is the closest sightline we have to the galaxy’s center where we can see the bubble being blown outward and energized.”

The COS observations also measure, for the first time, the composition of the material being swept up in the gaseous cloud. COS detected silicon, carbon, and aluminum, indicating that the gas is enriched in the heavy elements produced inside stars and represents the fossil remnants of star formation.

COS measured the temperature of the gas at approximately 17,500 degrees Fahrenheit, which is much cooler than most of the super-hot gas in the outflow, thought to be at about 18 million degrees Fahrenheit. “We are seeing cooler gas, perhaps interstellar gas in our galaxy’s disk, being swept up into that hot outflow,” Fox explained.

This is the first result in a survey of 20 faraway quasars whose light passes through gas inside or just outside the Fermi Bubbles — like a needle piercing a balloon. An analysis of the full sample will yield the amount of mass being ejected. The astronomers can then compare the outflow mass with the velocities at various locations in the bubbles to determine the amount of energy needed to drive the outburst and possibly the origin of the explosive event.

One possible cause for the outflows is a star-making frenzy near the galactic center that produces supernovas, which blow out gas. Another scenario is a star or a group of stars falling onto the Milky Way’s supermassive black hole. When that happens, gas superheated by the black hole blasts deep into space. Because the bubbles are short-lived compared to the age of our galaxy, it suggests this may be a repeating phenomenon in the Milky Way’s history. Whatever the trigger is, it likely occurs episodically, perhaps only when the black hole gobbles up a concentration of material.

“It looks like the outflows are a hiccup,” Fox said. “There may have been repeated ejections of material that have blown up, and we’re catching the latest one. By studying the light from the other quasars in our program, we may be able to detect the fossils of previous outflows.”

Galactic winds are common in star-forming galaxies, such as M82, which is furiously making stars in its core. “It looks like there’s a link between the amount of star formation and whether or not these outflows happen,” Fox said. “Although the Milky Way overall currently produces a moderate one to two stars a year, there is a high concentration of star formation close to the core of the galaxy.”

Source: Hubble Site