Tag Archives: astronomers

Artist’s impression of exocomets around Beta Pictoris. Credit: ESO

Two Families of Comets Found Around Nearby Star

Two Families of Comets Found Around Nearby Star


The HARPS instrument at ESO’s La Silla Observatory in Chile has been used to make the most complete census of comets around another star ever created. A French team of astronomers has studied nearly 500 individual comets orbiting the star Beta Pictoris and has discovered that they belong to two distinct families of exocomets: old exocomets that have made multiple passages near the star, and younger exocomets that probably came from the recent breakup of one or more larger objects. The new results will appear in the journal Nature on 23 October 2014.

Beta Pictoris is a young star located about 63 light-years from the Sun. It is only about 20 million years old and is surrounded by a huge disc of material — a very active young planetary system where gas and dust are produced by the evaporation of comets and the collisions of asteroids.

Artist’s impression of exocomets around Beta Pictoris. Credit: ESO
Artist’s impression of exocomets around Beta Pictoris. Credit: ESO

Flavien Kiefer (IAP/CNRS/UPMC), lead author of the new study sets the scene: “Beta Pictoris is a very exciting target! The detailed observations of its exocomets give us clues to help understand what processes occur in this kind of young planetary system.”

For almost 30 years astronomers have seen subtle changes in the light from Beta Pictoris that were thought to be caused by the passage of comets in front of the star itself. Comets are small bodies of a few kilometres in size, but they are rich in ices, which evaporate when they approach their star, producing gigantic tails of gas and dust that can absorb some of the light passing through them. The dim light from the exocomets is swamped by the light of the brilliant star so they cannot be imaged directly from Earth.

To study the Beta Pictoris exocomets, the team analysed more than 1000 observations obtained between 2003 and 2011 with the HARPS instrument on the ESO 3.6-metre telescope at the La Silla Observatory in Chile.

The researchers selected a sample of 493 different exocomets. Some exocomets were observed several times and for a few hours. Careful analysis provided measurements of the speed and the size of the gas clouds. Some of the orbital properties of each of these exocomets, such as the shape and the orientation of the orbit and the distance to the star, could also be deduced.

This analysis of several hundreds of exocomets in a single exo-planetary system is unique. It revealed the presence of two distinct families of exocomets: one family of old exocomets whose orbits are controlled by a massive planet [1], and another family, probably arising from the recent breakdown of one or a few bigger objects. Different families of comets also exist in the Solar System.

The exocomets of the first family have a variety of orbits and show a rather weak activity with low production rates of gas and dust. This suggests that these comets have exhausted their supplies of ices during their multiple passages close to Beta Pictoris [2].

The exocomets of the second family are much more active and are also on nearly identical orbits [3]. This suggests that the members of the second family all arise from the same origin: probably the breakdown of a larger object whose fragments are on an orbit grazing the star Beta Pictoris.

Flavien Kiefer concludes: “For the first time a statistical study has determined the physics and orbits for a large number of exocomets. This work provides a remarkable look at the mechanisms that were at work in the Solar System just after its formation 4.5 billion years ago.”

Notes

[1] A giant planet, Beta Pictoris b, has also been discovered in orbit at about a billion kilometres from the star and studied using high resolution images obtained with adaptive optics.

[2] Moreover, the orbits of these comets (eccentricity and orientation) are exactly as predicted for comets trapped inorbital resonance with a massive planet. The properties of the comets of the first family show that this planet in resonance must be at about 700 million kilometres from the star  — close to where the planet Beta Pictoris b was discovered.

[3] This makes them similar to the comets of the Kreutz family in the Solar System, or the fragments of Comet Shoemaker-Levy 9, which impacted Jupiter in July 1994.

Source: ESO

This is a temperature map of the "hot Jupiter" class exoplanet WASP 43b. The white-colored region on the daytime side is 2,800 degrees Fahrenheit. The nighttime side temperatures drop to under 1,000 degrees Fahrenheit.
Image Credit: NASA/ESA

NASA’s Hubble Maps the Temperature and Water Vapor on an Extreme Exoplanet

A team of scientists using NASA’s Hubble Space Telescope has made the most detailed global map yet of the glow from a turbulent planet outside our solar system, revealing its secrets of air temperatures and water vapor.

Hubble observations show the exoplanet, called WASP-43b, is no place to call home. It is a world of extremes, where seething winds howl at the speed of sound from a 3,000-degree-Fahrenheit “day” side, hot enough to melt steel, to a pitch-black “night” side with plunging temperatures below 1,000 degrees Fahrenheit.

This is a temperature map of the "hot Jupiter" class exoplanet WASP 43b. The white-colored region on the daytime side is 2,800 degrees Fahrenheit. The nighttime side temperatures drop to under 1,000 degrees Fahrenheit. Image Credit: NASA/ESA
This is a temperature map of the “hot Jupiter” class exoplanet WASP 43b. The white-colored region on the daytime side is 2,800 degrees Fahrenheit. The nighttime side temperatures drop to under 1,000 degrees Fahrenheit.
Image Credit: NASA/ESA

Astronomers have mapped the temperatures at different layers of the planet’s atmosphere and traced the amount and distribution of water vapor. The findings have ramifications for the understanding of atmospheric dynamics and how giant planets like Jupiter are formed.

“These measurements have opened the door for a new kinds of ways to compare the properties of different types of planets,” said team leader Jacob Bean of the University of Chicago.

First discovered in 2011, WASP-43b is located 260 light-years away. The planet is too distant to be photographed, but because its orbit is observed edge-on to Earth, astronomers detected it by observing regular dips in the light of its parent star as the planet passes in front of it.

“Our observations are the first of their kind in terms of providing a two-dimensional map on the longitude and altitude of the planet’s thermal structure that can be used to constrain atmospheric circulation and dynamical models for hot exoplanets,” said team member Kevin Stevenson of the University of Chicago.

As a hot ball of predominantly hydrogen gas, there are no surface features on the planet, such as oceans or continents that can be used to track its rotation. Only the severe temperature difference between the day and night sides can be used by a remote observer to mark the passage of a day on this world.

The planet is about the same size as Jupiter, but is nearly twice as dense. The planet is so close to its orange dwarf host star that it completes an orbit in just 19 hours. The planet also is gravitationally locked so that it keeps one hemisphere facing the star, just as our moon keeps one face toward Earth.

This was the first time astronomers were able to observe three complete rotations of any planet, which occurred during a span of four days. Scientists combined two previous methods of analyzing exoplanets in an unprecedented technique to study the atmosphere of WASP-43b. They used spectroscopy, dividing the planet’s light into its component colors, to determine the amount of water and the temperatures of the atmosphere. By observing the planet’s rotation, the astronomers also were able to precisely measure how the water is distributed at different longitudes.

Because there is no planet with these tortured conditions in our solar system, characterizing the atmosphere of such a bizarre world provides a unique laboratory for better understanding planet formation and planetary physics.

“The planet is so hot that all the water in its atmosphere is vaporized, rather than condensed into icy clouds like on Jupiter,” said team member Laura Kreidberg of the University of Chicago.

The amount of water in the giant planets of our solar system is poorly known because water that has precipitated out of the upper atmospheres of cool gas giant planets like Jupiter is locked away as ice. But so-called “hot Jupiters,” gas giants that have high surface temperatures because they orbit very close to their stars, water is in a vapor that can be readily traced.

“Water is thought to play an important role in the formation of giant planets, since comet-like bodies bombard young planets, delivering most of the water and other molecules that we can observe,” said Jonathan Fortney, a member of the team from the University of California, Santa Cruz.

In order to understand how giant planets form astronomers want to know how enriched they are in different elements. The team found that WASP-43b has about the same amount of water as we would expect for an object with the same chemical composition as our sun, shedding light on the fundamentals about how the planet formed. The team next aims to make water-abundance measurements for different planets.

The results are presented in two new papers, one published online in Science Express Thursday and the other published in The Astrophysical Journal Letters on Sept. 12.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center in Greenbelt, Maryland manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.

For images and more information about Hubble, visit:

http://www.nasa.gov/hubble

Source: NASA

Carolina’s Laura Mersini-Houghton shows that black holes do not exist

Carolina’s Laura Mersini-Houghton shows that black holes do not exist

 

The term black hole is entrenched in the English language. Can we let it go?

(Chapel Hill, N.C. – Sept. 23, 2014) Black holes have long captured the public imagination and been the subject of popular culture, from Star Trek to Hollywood. They are the ultimate unknown – the blackest and most dense objects in the universe that do not even let light escape. And as if they weren’t bizarre enough to begin with, now add this to the mix: they don’t exist.

By merging two seemingly conflicting theories, Laura Mersini-Houghton, a physics professor at UNC-Chapel Hill in the College of Arts and Sciences, has proven, mathematically, that black holes can never come into being in the first place. The work not only forces scientists to reimagine the fabric of space-time, but also rethink the origins of the universe.

“I’m still not over the shock,” said Mersini-Houghton. “We’ve been studying this problem for a more than 50 years and this solution gives us a lot to think about.”

For decades, black holes were thought to form when a massive star collapses under its own gravity to a single point in space – imagine the Earth being squished into a ball the size of a peanut – called a singularity. So the story went, an invisible membrane known as the event horizon surrounds the singularity and crossing this horizon means that you could never cross back. It’s the point where a black hole’s gravitational pull is so strong that nothing can escape it.

The reason black holes are so bizarre is that it pits two fundamental theories of the universe against each other. Einstein’s theory of gravity predicts the formation of black holes but a fundamental law of quantum theory states that no information from the universe can ever disappear. Efforts to combine these two theories lead to mathematical nonsense, and became known as the information loss paradox.

In 1974, Stephen Hawking used quantum mechanics to show that black holes emit radiation. Since then, scientists have detected fingerprints in the cosmos that are consistent with this radiation, identifying an ever-increasing list of the universe’s black holes.

But now Mersini-Houghton describes an entirely new scenario. She and Hawking both agree that as a star collapses under its own gravity, it produces Hawking radiation. However, in her new work, Mersini-Houghton shows that by giving off this radiation, the star also sheds mass. So much so that as it shrinks it no longer has the density to become a black hole.

Before a black hole can form, the dying star swells one last time and then explodes. A singularity never forms and neither does an event horizon. The take home message of her work is clear: there is no such thing as a black hole.

The paper, which was recently submitted to ArXiv, an online repository of physics papers that is not peer-reviewed, offers exact numerical solutions to this problem and was done in collaboration with Harald Peiffer, an expert on numerical relativity at the University of Toronto. An earlier paper, by Mersini-Houghton, originally submitted to ArXiv in June, was published in the journal Physics Letters B, and offers approximate solutions to the problem.

Experimental evidence may one day provide physical proof as to whether or not black holes exist in the universe. But for now, Mersini-Houghton says the mathematics are conclusive.

Many physicists and astronomers believe that our universe originated from a singularity that began expanding with the Big Bang. However, if singularities do not exist, then physicists have to rethink their ideas of the Big Bang and whether it ever happened.

“Physicists have been trying to merge these two theories – Einstein’s theory of gravity and quantum mechanics – for decades, but this scenario brings these two theories together, into harmony,” said Mersini-Houghton. “And that’s a big deal.”

-Carolina-

Mersini-Houghton’s ArXiv papers:

Approximate solutions:http://arxiv.org/abs/arXiv:1406.1525

Exact solutions:http://arxiv.org/abs/arXiv:1409.1837

Source: UNC News

Laser system

Physical constant is constant even in strong gravitational fields

An international team of physicists has shown that the mass ratio between protons and electrons is the same in weak and in very strong gravitational fields. Their study, which was partly funded by the FOM Foundation, is published online on 18 September 2014 in Physical Review Letters.


The idea that the laws of physics and its fundamental constants do not depend on local circumstances is called the equivalence principle. This principle is a cornerstone to Einstein’s theory of general relativity. To put the principle to the test, FOM physicists working at the LaserLaB at VU University Amsterdam determined whether one fundamental constant, the mass ratio between protons and electrons, depends on the strength of the gravitational field that the particles are in. Laser system

Laboratories on earth and in space 
The researchers compared the proton-electron mass ratio near the surface of a white dwarf star to the mass ratio in a laboratory on Earth. White dwarfs stars, which are in a late stage of their life cycle, have collapsed to less than one percent of their original size. The gravitational field at the surface of these stars is therefore much larger than that on earth, by a factor of 10,000. The physicists concluded that even these strong gravitational conditions, the proton-electron mass ratio is the same within a margin of 0.005 percent. In both cases, the proton mass is 1836.152672 times as big as the electron mass . 

Absorption spectra 
To reach their conclusion, the Dutch physicists collaborated with astronomers of the University of Leicester, the University of Cambridge and the Swinburne University of Technology in Melbourne. The team analysed absorption spectra of hydrogen molecules in white dwarf photospheres (the outer shell of a star from which light is radiated). The spectra were then compared to spectra obtained with a laser at LaserLaB in Amsterdam. 

Absorption spectra reveal which radiation frequencies are absorbed by a particle. A small deviation of the proton-electron mass ration would affect the structure of the molecule, and therefore the absorption spectrum as well. However, the comparison revealed that the spectra were very similar, which proves that the value of the proton-electron mass ratio is indeed independent of the strength of the gravitation field. 

Rock-solid 
FOM PhD student Julija Bagdonaite: “Previously, we confirmed the constancy of this fundamental constant on a cosmological time scale with the Very Large Telescope in Chile. Now we searched for a dependence on strong gravitational fields using the Hubble Space Telescope. Gradually we find that the fundamental constants seem to be rock-solid and eternal.”

Contact information Prof.dr. Wim Ubachs, LaserLaB VU University Amsterdam, +31 (0)20 598 79 48

Images The astronomical spectra were recorded with the Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope. For a picture of the COS, please visit the NASA website.

Reference Limits on a Gravitational field Dependence of the Proton-to-Electron Mass Ratio from H2 in White Dwarf Stars, Physical Review Letters, 18 September 2014.
Paper on ArXiv.  

Source: FOM

This image of the galaxy Messier 82 is a composite of data from the Chandra X-Ray Observatory, the Hubble Space Telescope and the Spitzer Space Telescope. The intermediate-mass black hole M82 X-1 is the brightest object in the inset, at approximately 2 o’clock near the galaxy’s center. Credit: NASA/H. Feng et al.

Fascinating rhythm: light pulses illuminate a rare black hole

The universe has so many black holes that it’s impossible to count them all. There may be 100 million of these intriguing astral objects in our galaxy alone. Nearly all black holes fall into one of two classes: big, and colossal. Astronomers know that black holes ranging from about 10 times to 100 times the mass of our sun are the remnants of dying stars, and that supermassive black holes, more than a million times the mass of the sun, inhabit the centers of most galaxies.

But scattered across the universe like oases in a desert are a few apparent black holes of a more mysterious type. Ranging from a hundred times to a few hundred thousand times the sun’s mass, these intermediate-mass black holes are so hard to measure that even their existence is sometimes disputed. Little is known about how they form. And some astronomers question whether they behave like other black holes.

Now a team of astronomers has succeeded in accurately measuring — and thus confirming the existence of — a black hole about 400 times the mass of our sun in a galaxy 12 million light years from Earth. The finding, by University of Maryland astronomy graduate student Dheeraj Pasham and two colleagues, was published online August 17 in the journal Nature.

Co-author Richard Mushotzky, a UMD astronomy professor, says the black hole in question is a just-right-sized version of this class of astral objects.

This image of the galaxy Messier 82 is a composite of data from the Chandra X-Ray Observatory, the Hubble Space Telescope and the Spitzer Space Telescope. The intermediate-mass black hole M82 X-1 is the brightest object in the inset, at approximately 2 o’clock near the galaxy’s center. Credit: NASA/H. Feng et al.
This image of the galaxy Messier 82 is a composite of data from the Chandra X-Ray Observatory, the Hubble Space Telescope and the Spitzer Space Telescope. The intermediate-mass black hole M82 X-1 is the brightest object in the inset, at approximately 2 o’clock near the galaxy’s center. Credit: NASA/H. Feng et al.

“Objects in this range are the least expected of all black holes,” says Mushotzky. “Astronomers have been asking, do these objects exist or do they not exist? What are their properties? Until now we have not had the data to answer these questions.” While the intermediate-mass black hole that the team studied is not the first one measured, it is the first one so precisely measured, Mushotzky says, “establishing it as a compelling example of this class of black holes.”

A black hole is a region in space containing a mass so dense that not even light can escape its gravity. Black holes are invisible, but astronomers can find them by tracking their gravitational pull on other objects. Matter being pulled into a black hole gathers around it like storm debris circling a tornado’s center. As this cosmic stuff rubs together it produces friction and light, making black holes among the universe’s brightest objects.

Since the 1970s astronomers have observed a few hundred objects that they thought were intermediate-mass black holes. But they couldn’t measure their mass, so they couldn’t be certain. “For reasons that are very hard to understand, these objects have resisted standard measurement techniques,” says Mushotzky.

Pasham, who will receive his Ph.D. in astronomy at UMD August 22, focused on one object in Messier 82, a galaxy in the constellation Ursa Major. Messier 82 is our closest “starburst galaxy,” where young stars are forming. Beginning in 1999 a NASA satellite telescope, the Chandra X-ray Observatory, detected X-rays in Messier 82 from a bright object prosaically dubbed M82 X-1. Astronomers, including Mushotzky and co-author Tod Strohmayer of NASA’s Goddard Space Flight Center, suspected for about a decade that the object was an intermediate-mass black hole, but estimates of its mass were not definitive enough to confirm that.

Between 2004 and 2010 NASA’s Rossi X-Ray Timing Explorer (RXTE) satellite telescope observed M82 X-1 about 800 times, recording individual x-ray particles emitted by the object. Pasham mapped the intensity and wavelength of x-rays in each sequence, then stitched the sequences together and analyzed the result.

Among the material circling the suspected black hole, he spotted two repeating flares of light. The flares showed a rhythmic pattern of light pulses, one occurring 5.1 times per second and the other 3.3 times per second – or a ratio of 3:2.

The two light oscillations were like two dust motes stuck in the grooves of a vinyl record spinning on a turntable, says Mushotzky. If the oscillations were musical beats, they would produce a specific syncopated rhythm. Think of a Latin-inflected bossa nova, or a tune from The Beatles’ White Album:

     “Mean Mister Mustard sleeps in the park, shaves in the dark, try’na save paper.”

In music, this is a 3:2 beat. Astronomers can use a 3:2 oscillation of light to measure a black hole’s massThe technique has been used on smaller black holes, but it has never before been applied to intermediate-mass black holes.

Pasham used the oscillations to estimate that M82 X-1 is 428 times the mass of the sun, give or take 105 solar masses. He does not propose an explanation for how this class of black holes formed. “We needed to confirm their existence observationally first,” he says. “Now the theorists can get to work.”

Though the Rossi telescope is no longer operational, NASA plans to launch a new X-ray telescope, the Neutron Star Interior Composition Explorer (NICER), in about two years. Pasham, who will begin a pot-doctoral research position at NASA Goddard in late August, has identified six potential intermediate-mass black holes that NICER might explore.

This work is based on observations made with the Rossi X-ray Timing Explorer (RXTE), managed and controlled by NASA’s Goddard Space Flight Center in Greenbelt, Md. The content of this article does not necessarily reflect the views of NASA or Goddard Space Flight Center.

Source: University of Maryland