Absorption Lines Shed New Light on 90 Year Old Puzzle

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Using the Gemini North Telescope, astronomers studying the central region of the Milky Way have discovered 13 diffuse interstellar bands with the longest wavelengths to date. The team’s discovery could someday solve a 90-year-old mystery about the existence of these bands.

“These diffuse interstellar bands—or DIBs—have never been seen before,” says Donald Figer, director of the Center for Detectors at Rochester Institute of Technology and one of the authors of a study appearing in the journal Nature.

What phenomenon are responsible for these absorption lines, and what impact do they have on our studies of our galaxy?

Figer offers his explanation of absorption lines, stating, “Spectra of stars have absorption lines because gas and dust along the line of sight to the stars absorb some of the light.”

Figer adds, “The most recent ideas are that diffuse interstellar bands are relatively simple carbon bearing molecules, similar to amino acids. Maybe these are amino acid chains in space, which supports the theory that the seeds of life originated in space and rained down on planets.”

“Observations in different Galactic sight lines indicate that the material responsible for these DIBs ‘survives’ under different physical conditions of temperature and density,” adds team member Paco Najarro (Center of Astrobiology, Madrid).

The discovery of low energy absorption lines by Figer and his team helps to determine the nature of diffuse interstellar bands. Figer believes that any future models that predict which wavelengths the particles absorb will have to include the newly discovered lower energies, stating, “We saw the same absorption lines in the spectra of every star. If we look at the exact wavelength of the features, we can figure out the kind of gas and dust between us and the stars that is absorbing the light.”

Spectra of the newly discovered Diffuse Interstellar Bands (DIB's).
Image Credit: Geballe, Najarro, Figer, Schlegelmilch, and de la Fuente.

Since their discovery 90 years ago, diffuse interstellar bands have been a mystery. To date, the known bands that have been identified before the team’s study occur mostly in visible wavelengths. Part of the puzzle is that the observed lines don’t match the predicted lines of simple molecules and can’t be traced to a single source.

“None of the diffuse interstellar bands has been convincingly identified with a specific element or molecule, and indeed their identification, individually and collectively, is one of the greatest challenges in astronomical spectroscopy, recent studies have suggested that DIB carriers are large carbon-containing molecules.” states lead author Thomas Geballe (Gemini Observatory).

One other benefit the newly discovered infrared bands offer is that they can be used to better understand the diffuse interstellar medium, where thick dust and gas normally block observations in visible light. By studying the stronger emissions, scientists may gain a better understanding of their molecular origin. So far, no research teams have been able to re-create the interstellar bands in a laboratory setting, mostly due to the difficulty of reproducing temperatures and pressure conditions the gas would experience in space.

If you’d like to learn more about the Gemini Observatory, visit: http://www.gemini.edu/
Read more about RIT’s Center for Detectors at: http://ridl.cis.rit.edu/

Source: Rochester Institute of Technology Press Release

Observing Alert: Bright Spot On Uranus Reported

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There’s nothing like a dynamic solar system… and right now another planet is being heard from. According to various sources, a bright spot – possibly a developing storm – has been spotted on Uranus.

“Professional observers this morning (October 27) reported a very bright cloud on Uranus, using the Gemini telescope, and need amateur confirmation if possible, to obtain a rotation period.” says John H. Rogers, Jupiter Section Director, British Astronomical Association. “Near-infrared filters may have the best chance of detecting it. It was recorded in the 1.6 micron band, which is further into the IR than amateurs can reach, but your usual near-IR filters might be successful. I think that methane filters are not especially promising, as these clouds on Uranus are overlaid by a methane-rich layer of atmosphere, but would be worth trying anyway. Anyone who has a 1-micron filter should have a go too.”

At this point in time, information is limited, but professional images taken using the 8.1-metre Gemini Telescope North on Hawaii have recorded a region said to be ten times brighter than the planetary background. The bright spot is believed to be attributed to methane ice. ““This is an H-band image, centered at 1.6 microns, close to the wavelength of maximum contrast for such features. Its contrast will decrease with decreasing wavelength, and will likely not be detectable by amateur astronomers, except possibly at the longer CCD wavelengths where the Rayleigh scattering background can be suppressed.” says Larry Sromovsky, of the University of Wisconsin-Madison. “Looking with a methane band filters at 890 nm might be productive, especially if the feature continues to brighten.”

“The feature is not very large; instead its prominence is due to its high altitude, placing it above the intense absorption of methane in the deeper atmosphere. This is much higher than the 1.2-bar methane condensation level and thus it is expected to be predominantly composed of methane ice particles.”

Dr Sromovsky added: “The latitude of the feature is approximately 22.5° north planetocentric, which is a latitude nearly at rest with respect to the interior. So it should rotate around Uranus’ axis with nearly a 17.24-hour period. At the time of the image, the feature’s longitude was 351° West. That could change slowly in either direction.

“The low latitude is unusual. Previous exceptionally bright cloud features on Uranus were at close to 30° North, both in 1998 (Sromovsky et al. 2000, Icarus 146, 307-311) and in 2005 (Sromovsky et al. 2007, Icarus 192, 558-575). The 2005 feature oscillated ±1° about its mean latitude. The new feature might also oscillate in latitude, in which case its longitudinal drift rate might also vary with time.”

Hang in there, UT readers! Right now we have two of our best astrophotographers doing their best to give us an exclusive look! This page will be updated as more information becomes available.

Partial Quote Source: Skymania News Release.

Spectacular Galaxies Dancing Towards Destruction

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More than just another pretty picture? I’ll say! This beautiful image of the galaxy pair NGC 6872 and IC 4970 was part of a competition for high school students in Australia to obtain scientifically useful (and aesthetically pleasing) images using the Gemini Observatory. The winners were students from the Sydney Girls High School Astronomy Club in central Sydney, who proposed that Gemini investigate these two galaxies that are embraced in a graceful galactic dance that, — as the team described in the essay to support their entry — “…will also serve to illustrate the situation faced by the Milky Way and the Andromeda galaxy in millions of years.”

We can only hope we look this pretty millions of years from now!

This image shows what happens when galaxies interact, and how the gravitational forces distort and tear away at their original structure. Spiral galaxies can have their arms elongate out to enormous distances: in NGC 6872, the arms have been stretched out to span hundreds of thousands of light-years—many times further than the spiral arms of our own Milky Way galaxy. Over hundreds of millions of years, NGC 6872’s arms will fall back toward the central part of the galaxy, and the companion galaxy (IC 4970) will eventually be merged into NGC 6872.

But that will be another pretty picture, as galaxy mergers often leads to a burst of new star formation. Already, the blue light of recently created star clusters dot the outer reaches of NGC 6872’s elongated arms. Dark fingers of dust and gas along the arms soak up the visible light. That dust and gas is the raw material out of which future generations of stars could be born.

Members of the SGHS Astronomy Club Executive Council receiving the Gemini image on behalf of the entire club. Photo credit: Australian Gemini Office.

Learn more about the contest and the winning team at this article on the Gemini website. Also, a new contest is underway for Australian students in 2011, and more details can be found at this link.

Source: Gemini Observatory

Mystery Object Found Orbiting Brown Dwarf

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Big planet or companion brown dwarf? Using the Hubble Space Telescope and the Gemini Observatory, astronomers have discovered an unusual object orbiting a brown dwarf, and its discovery could fuel additional debate about what exactly constitutes a planet. The object circles a nearby brown dwarf in the Taurus star-forming region with an orbit approximately 3.6 billion kilometers (2.25 billion miles) out, about the same as Saturn from our sun. The astronomers say it is the right size for a planet, but they believe the object formed in less than 1 million years — the approximate age of the brown dwarf — and much faster than the predicted time it takes to build planets according to conventional theories.

Kamen Todorov of Penn State University and his team conducted a survey of 32 young brown dwarfs in the Taurus region.

The object orbits the brown dwarf 2M J044144 and is about 5-10 times the mass of Jupiter. Brown dwarfs are objects that typically are tens of times the mass of Jupiter and are too small to sustain nuclear fusion to shine as stars do.

Artist's conception of the binary system 2M J044144. Science Credit: NASA, ESA, and K. Todorov and K. Luman (Penn State University) Artwork Credit: Gemini Observatory, courtesy of L. Cook

While there has been a lot of discussion in the context of the Pluto debate over how small an object can be and still be called a planet, this new observation addresses the question at the other end of the size spectrum: How small can an object be and still be a brown dwarf rather than a planet? This new companion is within the range of masses observed for planets around stars, but again, the astronomers aren’t sure if it is a planet or a companion brown dwarf star.

The answer is strongly connected to the mechanism by which the companion most likely formed.

The Hubble new release offers these three possible scenarios for how the object may have formed:

Dust in a circumstellar disk slowly agglomerates to form a rocky planet 10 times larger than Earth, which then accumulates a large gaseous envelope; a lump of gas in the disk quickly collapses to form an object the size of a gas giant planet; or, rather than forming in a disk, a companion forms directly from the collapse of the vast cloud of gas and dust in the same manner as a star (or brown dwarf).

If the last scenario is correct, then this discovery demonstrates that planetary-mass bodies can be made through the same mechanism that builds stars. This is the likely solution because the companion is too young to have formed by the first scenario, which is very slow. The second mechanism occurs rapidly, but the disk around the central brown dwarf probably did not contain enough material to make an object with a mass of 5-10 Jupiter masses.

“The most interesting implication of this result is that it shows that the process that makes binary stars extends all the way down to planetary masses. So it appears that nature is able to make planetary-mass companions through two very different mechanisms,” said team member Kevin Luhman of the Center for Exoplanets and Habitable Worlds at Penn State University.

If the mystery companion formed through cloud collapse and fragmentation, as stellar binary systems do, then it is not a planet by definition because planets build up inside disks.

The mass of the companion is estimated by comparing its brightness to the luminosities predicted by theoretical evolutionary models for objects at various masses for an age of 1 million years.

Further supporting evidence comes from the presence of a very nearby binary system that contains a small red star and a brown dwarf. Luhman thinks that all four objects may have formed in the same cloud collapse, making this in actuality a quadruple system.

“The configuration closely resembles quadruple star systems, suggesting that all of its components formed like stars,” he said.

The team’s research is being published in an upcoming issue of The Astrophysical Journal.

The team’s paper: Discovery of a Planetary-Mass Companion to a Brown Dwarf in Taurus

Source: HubbleSite