Space Telescopes Provide New Look at 2,000 Year Old Supernova

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What caused a huge explosion nearly 2,000 years ago, seen by early Chinese astronomers? Scientists have long known that a “guest star” that had mysteriously appeared in the sky and stayed for about 8 months in the year 185 was the first documented supernova. But now the combined efforts of four space observatories have provided insight into this stellar explosion and why it was so huge – and why its shattered remains — the object known as RCW 86 – is now spread out to great distances.

“This supernova remnant got really big, really fast,” said Brian Williams, an astronomer at North Carolina State University in Raleigh. “It’s two to three times bigger than we would expect for a supernova that was witnessed exploding nearly 2,000 years ago. Now, we’ve been able to finally pinpoint the cause.”

By studying new infrared observations from the Spitzer Space Telescope and data from the Wide-field Infrared Survey Explorer, and previous data from NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton Observatory, astronomers were able to determine that the ancient supernova was a Type Ia supernova. And doing some “forensics” on the stellar remains, the astronomers could piece together that prior to exploding, winds from the white dwarf cleared out a huge “cavity,” a region of very low-density surrounding the system. The explosion into this cavity was able to expand much faster than it otherwise would have. The ejected material would have traveled into the cavity, unimpeded by gas and dust and spread out quickly.

This is the first time that astronomers have been able to deduce that this type of cavity was created, and scientists say the results may have significant implications for theories of white-dwarf binary systems and Type Ia supernovae.

At about 85 light-years in diameter, RCW occupies a region of the sky that is slightly larger than the full moon. It lies in the southern constellation of Circinus.

Source: JPL

Failed Star Is One Cool Companion

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Astronomers have located a planet-like star that’s barely warmer than a balmy summer day on Earth… it’s literally the coldest object ever directly imaged outside of our solar system!

WD 0806-661 B is a brown “Y dwarf” star that’s a member of a binary pair. Its companion is a much hotter white dwarf, the remains of a Sun-like star that has shed its outer layers. The pair is located about 63 light-years away, which is pretty close to us as stars go. The stars were identified by a team led by Penn State Associate Professor of Astronomy and Astrophysics Kevin Luhman using images from NASA’s Spitzer Space Telescope. Two infrared images taken in 2004 and 2009 were overlaid on top of each other and show the stars moving in tandem, indicating a shared orbit.

These two infrared images were taken by the Spitzer Space Telescope in 2004 and 2009. They show a faint object moving through space together with a white dwarf. Credit: Kevin Luhman, Penn State University, October 2011. (Click to play.)

Of course, locating the stars wasn’t quite as easy as that. To find this stellar duo Luhman and his team searched through over six hundred images of stars located near our solar system taken years apart, looking for any shifting position as a pair.

The use of infrared imaging allowed the team to locate a dim brown dwarf star like WD 0806-661 B, which emits little visible light but shines brightly in infrared. (Even though brown dwarfs are extremely cool for stars they are still much warmer than the surrounding space. And, for the record, brown dwarfs are not actually brown.) Measurements estimate the temperature of WD 0806-661 B to be in the range of about 80 to 130 degrees Fahrenheit (26 to 54 degrees C, or 300 – 345 K)… literally body temperature!

“Essentially, what we have found is a very small star with an atmospheric temperature about cool as the Earth’s.”

– Kevin Luhman, Associate Professor of Astronomy and Astrophysics, Penn State

Six to nine times the mass of Jupiter, WD 0806-661 B is more like a planet than a star. It never accumulated enough mass to ignite thermonuclear reactions and thus more resembles a gas giant like Jupiter or Saturn. But its origins are most likely star-like, as its distance from its white dwarf companion – about 2,500 astronomical units – indicates that it developed on its own rather than forming from the other star’s disc.

There is a small chance, though, that it did form as a planet and gradually migrated out to its current distance. More research will help determine whether this may have been the case.

Brown dwarfs, first discovered in 1995, are valuable research targets because they are the next best thing to studying cool atmospheres on planets outside our solar system. Scientists keep trying to locate new record-holders for the coldest brown dwarfs, and with the discovery of WD 0806-661 B Luhman’s team has done just that!

A paper covering the team’s findings will be published in The Astrophysical Journal. Other authors of the paper include Ivo Labbé, Andrew J. Monson and Eric Persson of the Observatories of the Carnegie Institution for Science, Pasadena, Calif.; Didier Saumon of the Los Alamos National Laboratory, New Mexico; Mark S. Marley of the NASA Ames Research Center, Moffett Field, Calif.; and John J. Bochanski also of The Pennsylvania State University.

Read more on the Penn State science site here.

 

Ancient Galaxies Fed On Gas, Not Collisions

[/caption]The traditional picture of galaxy growth is not pretty. In fact, it’s a kind of cosmic cannibalism: two galaxies are caught in ominous tango, eventually melding together in a fiery collision, thus spurring on an intense but short-lived bout of star formation. Now, new research suggests that most galaxies in the early Universe increased their stellar populations in a considerably less violent way, simply by burning through their own gas over long periods of time.

The research was conducted by a group of astronomers at NASA’s Spitzer Science Center in Pasadena, California. The team used the Spitzer Space Telescope to peer at 70 distant galaxies that flourished when the Universe was only 1-2 billion years old. The spectra of 70% of these galaxies showed an abundance of H alpha, an excited form of hydrogen gas that is prevalent in busy star-forming regions. Today, only one out of every thousand galaxies carries such an abundance of H alpha; in fact, the team estimates that star formation in the early Universe outpaced that of today by a factor of 100!

This split view shows how a normal spiral galaxy around our local universe (left) might have looked back in the distant universe, when astronomers think galaxies would have been filled with larger populations of hot, bright stars (right). Image credit: NASA/JPL-Caltech/STScI

Not only did these early galaxies crank out stars much faster than their modern-day counterparts, but they created much larger stars as well. By grazing on their own stores of gas, galaxies from this epoch routinely formed stars up to 100 solar masses in size.

These impressive bouts of star formation occurred over the course of hundreds of millions of years. The extremely long time scales involved suggest that while they probably played a minor role, galaxy mergers were not the main precursor to star formation in the Universe’s younger years. “This type of galactic cannibalism was rare,” said Ranga-Ram Chary, a member of the team. “Instead, we are seeing evidence for a mechanism of galaxy growth in which a typical galaxy fed itself through a steady stream of gas, making stars at a much faster rate than previously thought.” Even on cosmic scales, it would seem that slow and steady really does win the race.

Source: JPL

Kepler Team Announces New Rocky Planet

 

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Today at the American Astronomical Society conference in Boston, the Kepler team announced the confirmation of a new rocky planet in orbit around Kepler-10. Dubbed Kepler-10c, this planet is described as a “scorched, molten Earth.”

2.2 times the radius of Earth, Kepler-10c orbits its star every 45 days. Both it and its smaller, previously-discovered sibling 10b are located too close to their star for liquid water to exist.

Kepler-10c was validated using a new computer simulation technique called “Blender” as well as additional infrared data from NASA’s Spitzer Space Telescope. This method can be used to locate Earth-sized planets within Kepler’s field of view and could also potentially help find Earth-sized planets within other stars’ habitable zones.

This is the first time the team feels sure that it has exhaustively ruled out alternative explanations for dips in the brightness of a star… basically, they are 99.998% sure that Kepler-10c exists.

The Kepler-10 star system is located about 560 light-years away near the Cygnus and Lyra constellations.

Read the release on the Nature.com blog.

Image credit: NASA/Ames/JPL-Caltech

Spitzer Captures a Pink Sunflower in Space

Classifying Galaxies

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Looking out my own window this morning provides a gloomy overcast view, so this new image from the Spitzer Space Telescope provides a day-brightener: a pink sunflower! This is the Sunflower galaxy, also known as Messier 63, and with Spitzers’ infrared eyes, the arms of the galaxy show up vividly. Infrared light is sensitive to the dust lanes in spiral galaxies, which appear dark in visible-light images. Spitzer’s view reveals complex structures that trace the galaxy’s spiral arm pattern.

Source: JPL
This galaxy is about 37 million-light years away from Earth, and lies close to the well-known Whirlpool galaxy and the associated Messier 51 group of galaxies.

Astronomy Cast Ep. 207: Lyman Spitzer

Lyman Spitzer

Time for another action-packed double episode of Astronomy Cast. This week we focus on the Lyman Spitzer, a theoretical physicist and astronomer who worked on star formation and plasma physics. Of course, this will lead us into next week’s episode where we talk about the mission that bears his name: the Spitzer Space Telescope.

Click here to download the episode

Lyman Spitzer – Show notes and transcript

Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

Near Earth Asteroids Vary Widely in Composition, Origin

Eros Asteroid

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From the Spitzer website:

New research from NASA’s Spitzer Space Telescope reveals that asteroids somewhat near Earth, termed near-Earth objects, are a mixed bunch, with a surprisingly wide array of compositions. Like a piñata filled with everything from chocolates to fruity candies, these asteroids come in assorted colors and compositions. Some are dark and dull; others are shiny and bright. The Spitzer observations of 100 known near-Earth asteroids demonstrate that the objects’ diversity is greater than previously thought.

The findings are helping astronomers better understand near-Earth objects as a whole — a population whose physical properties are not well known.

“These rocks are teaching us about the places they come from,” said David Trilling of Northern Arizona University, Flagstaff, lead author of a new paper on the research appearing in the September issue of Astronomical Journal. “It’s like studying pebbles in a streambed to learn about the mountains they tumbled down.”

After nearly six years of operation, in May 2009, Spitzer used up the liquid coolant needed to chill its infrared detectors. It is now operating in a so-called “warm” mode (the actual temperature is still quite cold at 30 Kelvin, or minus 406 degrees Fahrenheit). Two of Spitzer’s infrared channels, the shortest-wavelength detectors on the observatory, are working perfectly.

One of the mission’s new “warm” programs is to survey about 700 near-Earth objects, cataloging their individual traits. By observing in infrared, Spitzer is helping to gather more accurate estimates of asteroids’ compositions and sizes than what is possible with visible light alone. Visible-light observations of an asteroid won’t differentiate between an asteroid that is big and dark, or small and light. Both rocks would reflect the same amount of visible sunlight. Infrared data provide a read on the object’s temperature, which then tells an astronomer more about the actual size and composition. A big, dark rock has a higher temperature than a small, light one because it absorbs more sunlight.

Trilling and his team have analyzed preliminary data on 100 near-Earth asteroids so far. They plan to observe 600 more over the next year. There are roughly 7,000 known near-Earth objects out of a population expected to number in the tens to hundreds of thousands.

“Very little is known about the physical characteristics of the near-Earth population,” said Trilling. “Our data will tell us more about the population, and how it changes from one object to the next. This information could be used to help plan possible future space missions to study a near-Earth object.”

The data show that some of the smaller objects have surprisingly high albedos (an albedo is a measurement of how much sunlight an object reflects). Since asteroid surfaces become darker with time due to exposure to solar radiation, the presence of lighter, brighter surfaces for some asteroids may indicate that they are relatively young. This is evidence for the continuing evolution of the near-Earth object population.

In addition, the fact that the asteroids observed so far have a greater degree of diversity than expected indicates that they might have different origins. Some might come from the main belt between Mars and Jupiter, and others could come from farther out in the solar system. This diversity also suggests that the materials that went into making the asteroids — the same materials that make up our planets — were probably mixed together like a big solar-system soup very early in its history.

The research complements that of NASA’s Wide-field Infrared Survey Explorer, or WISE, an all-sky infrared survey mission also up in space now. WISE has already observed more than 430 near-Earth objects — of these, more than 110 are newly discovered.

In the future, both Spitzer and WISE will tell us even more about the “flavors” of near-Earth objects. This could reveal new clues about how the cosmic objects might have dotted our young planet with water and organics — ingredients needed to kick-start life.

Big or Small, All Stars Form the Same Way

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How do massive stars form? This has been one of the more hotly debated questions in astronomy. Do big stars form by accretion like low-mass stars or do they form through the merging of low mass protostars? Since massive stars tend to be quite far away and usually are surrounded by a shroud of dust, they are difficult to observe, said Stefan Kraus from the University of Michigan. But Kraus and his team have obtained the first image of a dusty disc closely encircling a massive baby star, providing direct evidence that, big or small, all stars form the same way.

“Our observations show a disc surrounding an embryonic young, massive star, which is now fully formed,” said Kraus. “It’s the first time something like this has been observed, and the disk very much resembles what we see around young stars that are much smaller, except everything is scaled up and more massive.”

Not only that, but Kraus and his team found hints at a potential planet-forming region around the nascent star.

Using ESO’s Very Large Telescope Interferometer Kraus and his team focused on IRAS 13481-6124, a star located about 10,000 light-years away in the constellation Centaurus, and about 20 times more massive than our sun. “We were able to get a very sharp view into the innermost regions around this star by combining the light of separate telescopes,” Kraus said, “basically mimicking the resolving power of a telescope with an incredible 85-meter (280-foot) mirror.”

Kraus added that the resulting resolution is about 2.4 milliarcseconds, which is equivalent to picking out the head of a screw on the International Space Station from Earth, or more than ten times the resolution possible with current visible-light telescopes in space.

They also made complementary observations with the 3.58-meter New Technology Telescope at La Silla. The team chose this region by looking at archived images from the Spitzer Space Telescope as well as from observations done with the APEX 12-meter submillimeter telescope, where they discovered the presence of a jet.

“Such jets are commonly observed around young low-mass stars and generally indicate the presence of a disc,” says Kraus.

Astronomers have obtained the first clear look at a dusty disk closely encircling a massive baby star, providing direct evidence that massive stars do form in the same way as their smaller brethren -- and closing an enduring debate. This artist's concept shows what such a massive disk might look like. Image credit: ESO/L. Calçada

From their observations, the team believes the system is about 60,000 years old, and that the star has reached its final mass. Because of the intense light of the star — 30,000 times more luminous than our Sun — the disc will soon start to evaporate. The disc extends to about 130 times the Earth–Sun distance — or 130 astronomical units (AU) — and has a mass similar to that of the star, roughly twenty times the Sun. In addition, the inner parts of the disc are shown to be devoid of dust, which could mean that planets are forming around the star.

“In the future, we might be able to see gaps in this and other dust disks created by orbiting planets, although it is unlikely that such bodies could survive for long,” Kraus said. “A planet around such a massive star would be destroyed by the strong stellar winds and intense radiation as soon as the protective disk material is gone, which leaves little chance for the development of solar systems like our own.”

Kraus looks forward to observations with the Atacama Large Millimeter/submillimeter Array (ALMA), currently under construction in Chile, which may be able to resolve the disks to an even sharper resolution.

Previously, Spitzer detected dusty disks of planetary debris around more mature massive stars, which supports the idea that planets may form even in these extreme environments. (Read about that research here.) .

Sources: ESO, JPL

Spitzer Spies Earliest Black Holes

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The Spitzer Space Telescope has found what appear to be two of the earliest and most primitive supermassive black holes known. “We have found what are likely first-generation quasars, born in a dust-free medium and at the earliest stages of evolution,” said Linhua Jiang of the University of Arizona, Tucson, lead author of a paper published this week in Nature.

A quasar is a compact region in the center of a massive galaxy surrounding the central supermassive black hole.

As shown by the image we posted earlier today from the Planck mission, our galaxy – and the Universe – is littered with dust. But scientists believe the very early universe didn’t have any dust — which tells them that the most primitive quasars should also be dust-free. But nobody had seen any “clean” quasars — until now.

Spitzer has identified two — the smallest on record — about 13 billion light-years away from Earth. The quasars, called J0005-0006 and J0303-0019, were first unveiled in visible light using data from the Sloan Digital Sky Survey. That discovery team, which included Jiang, was led by Xiaohui Fan, a coauthor of the recent paper. NASA’s Chandra X-ray Observatory had also observed X-rays from one of the objects. X-rays, ultraviolet and optical light stream out from quasars as the gas surrounding them is swallowed.

“Quasars emit an enormous amount of light, making them detectable literally at the edge of the observable universe,” said Fan.

These two data plots from NASA's Spitzer Space Telescope show a primitive supermassive black hole (top) compared to a typical one. Image credit: NASA/JPL-Caltech

When Jiang and his colleagues set out to observe J0005-0006 and J0303-0019 with Spitzer between 2006 and 2009, their targets didn’t stand out much from the usual quasar bunch. Spitzer measured infrared light from the objects along with 19 others, all belonging to a class of the most distant quasars known. Each quasar is anchored by a supermassive black hole weighing more than 100 million suns.

Of the 21 quasars, J0005-0006 and J0303-0019 lacked characteristic signatures of hot dust, the Spitzer data showed. Spitzer’s infrared sight makes the space telescope ideally suited to detect the warm glow of dust that has been heated by feeding black holes.

“We think these early black holes are forming around the time when the dust was first forming in the universe, less than one billion years after the Big Bang,” said Fan. “The primordial universe did not contain any molecules that could coagulate to form dust. The elements necessary for this process were produced and pumped into the universe later by stars.”

The astronomers also observed that the amount of hot dust in a quasar goes up with the mass of its black hole. As a black hole grows, dust has more time to materialize around it. The black holes at the cores of J0005-0006 and J0303-0019 have the smallest measured masses known in the early universe, indicating they are particularly young, and at a stage when dust has not yet formed around them.

The Spitzer observations were made before the telescope ran out of its liquid coolant in May 2009, beginning its “warm” mission.

Source: JPL

This Week’s astro-ph Preprints: Jean Tate’s Best Pick

It goes by the super-catchy (not!) title “A Catalog of MIPSGAL Disk and Ring Sources”. I chose it, over 213 competitors, because it’s pure astronomy, and because it’s something you don’t need a PhD to be able to do, or even a BSc.

Oh, and also because Don Mizuno and co-authors may have found two, quite local, spiral galaxies that no one has ever seen before!

Some quick background: arXiv has been going for several years now, and provides preprints, on the web, of papers “in the fields of physics, mathematics, non-linear science, computer science, quantitative biology and statistics”. It’s owned, operated and funded by Cornell University. astro-ph is the collection of preprints classified as astro physics; the “recent” category in astro-ph is the new preprints submitted in the last week.

When I have any, one of my favorite spare-time activities is browsing astro-ph (Hey, I did say, in my profile, that I am hooked on astronomy!)

Briefly, what Mizuno and his co-authors did was get hold of some of the images from Spitzer (something that anyone can do, provided their internet connection has enough bandwidth), and eyeball them, looking for things which look like disks and rings. Having found over 400 of them, they did what the human brain does superbly well: they grouped them by similarity of appearance, and gave the groups names. They then checked out other images – from different parts of Spitzer’s archive, and from IRAS – and checked to see how many had already been cataloged.

And what did they find? Well, first, that most of the objects they found had not been cataloged before, and certainly not given definite classifications! Many, perhaps most, of the new objects are planetary nebulae, and their findings may help address a long-standing puzzle in this part of astronomy.

MGE314.2378+00.9793 (Mizuno et al./Spitzer)
MGE351.2381-00.0145 (Mizuno et al./Spitzer)

But they also may have found two local spiral galaxies, which had not been noticed before because they are obscured by the gas-and-dust clouds in the Milky Way plane. How cool is that!

Here’s the ‘credits’ section of the preprint: “This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA in part through an award issued by JPL/Caltech. This research made use of the SIMBAD database and the Vizier catalog access tool, operated by the Centre de Donnees Astronomique de Strasbourg. This research has also made use of NASA’s Astrophysics Data System Bibliographic Services.”

And here’s the preprint itself: arXiv:1002.4221 A Catalog of MIPSGAL Disk and Ring Sources; D.R. Mizuno(1), K. E. Kraemer(2), N. Flagey(3), N. Billot(4), S. Shenoy(5), R. Paladini(3), E. Ryan(6), A. Noriega-Crespo(3), S. J. Carey(3). ((1) Institute for Scientific Research, (2) Air Force Research Laboratory, (3) Spitzer Science Center, (4) NASA Herschel Science Center, (5) Ames Research Center, (6) University of Minnesota)

PS, going over the Astronomy Cast episode How to be Taken Seriously by Scientists is what motivated me to pick this preprint (however, I must tell you, in all honesty, that there are at least ten other preprints that are equally pickable).