Category: Astronomy

The Milky Way’s nucleus. Sagittarius A* is the bright white dot at center. Image credit: NRAO/AUI/NSF, Jun-Hui Zhao, W.M. Goss. Click to enlarge.
Astronomers have gotten their deepest glimpse into the heart of our Milky Way Galaxy, peering closer to the supermassive black hole at the Galaxy’s core then ever before. Using the National Science Foundation’s continent-wide Very Long Baseline Array (VLBA), they found that a radio-wave-emitting object at the Galaxy’s center would nearly fit between the Earth and the Sun. This is half the size measured in any previous observation.

“We’re getting tantalizingly close to being able to see an unmistakable signature that would provide the first concrete proof of a supermassive black hole at a galaxy’s center,” said Zhi-Qiang Shen, of the Shanghai Astronomical Observatory and the Chinese Academy of Sciences. A black hole is a concentration of mass so dense that not even light can escape its powerful gravitational pull.

The astronomers used the VLBA to measure the size of an object called Sagittarius A* (pronounced “A-star”) that marks the exact center of our Galaxy. Last year, a different team announced that their measurements showed the object would fit inside the complete circle of Earth’s orbit around the Sun. Shen and his team, by observing at a higher radio frequency, measured Sagittarius A* as half that size.

A mass equal to four million Suns is known to lie within Sagittarius A*, and the new measurement makes the case for a black hole even more compelling than it was previously. Scientists simply don’t know of any long-lasting object other than a black hole that could contain this much mass in such a small area. However, they would like to see even stronger proof of a black hole.

“The extremely strong gravitational pull of a black hole has several effects that would produce a distinctive ‘shadow’ that we think we could see if we can image details about half as small as those in our latest images,” said Fred K.Y. Lo, Director of the National Radio Astronomy Observatory and another member of the research team. “Seeing that shadow would be the final proof that a supermassive black hole is at the center of our Galaxy,” Lo added.

Many galaxies are believed to have supermassive black holes at their centers, and many of these are much more massive than the Milky Way’s black hole. The Milky Way’s central black hole is much less active than that of many other galaxies, presumably because it has less nearby material to “eat.” Astronomers believe that the radio waves they see coming from Sagittarius A* are either generated by particle jets that have been detected in many more-active galaxies or from accretion flows that are spiraling into the central black hole. By observing the object at higher radio frequencies, scientists have detected a region of radiation ever closer to the black hole. The results announced last year were based on observations at 43 GigaHertz (GHz), and the latest observations were made at 86 GHz.

“We believe that if we can double the frequency again, we will see the black-hole shadow produced by effects of Einstein’s General Relativity theory,” Lo said.

In a few years, when the Atacama Large Millimeter Array (ALMA) comes on line, it may be used in conjunction with other millimeter-wave telescopes to make the higher-frequency observations that will reveal the telltale black-hole shadow.

At a distance of 26,000 light-years, the Milky Way’s central black hole is the closest such supermassive object. That makes it the most likely one to finally reveal the concrete evidence for a black hole that astronomers have sought for years.

Shen and Lo worked with Mao-Chang Liang of Caltech, Paul Ho of the Harvard-Smithsonian Center for Astrophysics (CfA) and the Institute of Astronomy & Astrophysics of the Academia Sinica in Taiwan, and Jun-Hui Zhao of CfA. The astronomers published their findings in the November 3 issue of the scientific journal Nature.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Original Source: NRAO News Release

Artist illustration of the early Universe. Image credit: NASA/JPL-Caltech/R. Hurt (SSC). Click to enlarge.
Scientists using NASA’s Spitzer Space Telescope say they have detected light that may be from the earliest objects in the universe. If confirmed, the observation provides a glimpse of an era more than 13 billion years ago when, after the fading embers of the theorized Big Bang gave way to millions of years of pervasive darkness, the universe came alive.

This light could be from the very first stars or perhaps from hot gas falling into the first black holes. The science team, based at NASA Goddard Space Flight Center in Greenbelt, Md., describes the observation as seeing the glow of a distant city at night from an airplane. The light is too distant and feeble to resolve individual objects.

“We think we are seeing the collective light from millions of the first objects to form in the universe,” said Dr. Alexander Kashlinsky, Science Systems and Applications scientist and lead author on the Nature article that appeared in the Nov. 3 issue. “The objects disappeared eons ago, yet their light is still traveling across the universe.”

Scientists theorize that space, time and matter originated 13.7 billion years ago in a Big Bang. Another 200 million years would pass before the era of first starlight. A 10-hour observation by Spitzer’s infrared array camera in the constellation Draco captured a diffuse glow of infrared light, lower in energy than optical light and invisible to us. The Goddard team says that this glow is likely from Population III stars, a hypothesized class of stars thought to have formed before all others. (Population I and II stars, named by order of their discovery, comprise the familiar types of stars we see at night.)

Theorists say the first stars were likely over a hundred times more massive than Earth’s sun and extremely hot, bright, and short-lived, each one burning for only a few million years. The ultraviolet light that Population III stars emitted would be redshifted, or stretched to lower energies, by the universe’s expansion. That light should now be detectable in the infrared.

“This deep observation was filled with familiar-looking stars and galaxies,” said Dr. John Mather, senior project scientist for JWST and a co-author on the Nature article. “We removed everything we knew—all the stars and galaxies both near and far. We were left with a picture of part of the sky with no stars or galaxies, but it still had this infrared glow with giant blobs that we think could be the glow from the very first stars.”

This new Spitzer discovery agrees with observations from the NASA Cosmic Background Explorer (COBE) satellite from the 1990s that suggested there may be an infrared background that could not be attributed to known stars. It also supports observations from the NASA Wilkinson Microwave Anisotropy Probe from 2003, which estimated that stars first ignited 200 million to 400 million years after the Big Bang.

“This difficult measurement pushes the instrument to performance limits that were not anticipated in its design,” said team member Dr. S. Harvey Moseley, instrument scientist for Spitzer. “We have worked very hard to rule out other sources for the signal we observed.”

The low noise and high resolution of Spitzer’s infrared array camera enabled the team to remove the fog of foreground galaxies, made of later stellar populations, until the cumulative light from the first light dominated the signal on large angular scales. The team, which also includes Dr. Richard Arendt, Science Systems and Applications scientist, noted that future missions, such as NASA’s James Webb Space Telescope, will find the first individual clumps of these stars or the individual exploding stars that might have made the first black holes.

This analysis was partially funded through the National Science Foundation. The Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. NASA Goddard built Spitzer’s infrared array camera which took the observations. The instrument’s principal investigator is Dr. Giovanni Fazio, Smithsonian Astrophysical Observatory, Cambridge, Mass.

Original Source: Spitzer News Release

Eta Carinae. Image credit: Hubble. Click to enlarge.
Scientists using NASA’s Far Ultraviolet Spectroscopic Explorer satellite made the first direct detection of a companion star of Eta Carinae. Eta Carinae is one of the most massive and unusual stars in the Milky Way galaxy. The detection was made possible by the high temperature of the companion star and the unique sensitivity of the satellite at the shortest ultraviolet wavelengths.

Eta Carinae is an unstable star thought to be rapidly approaching the final stage of its life. It is clearly visible from the southern hemisphere and has been the subject of intense studies for decades. This mysterious star is located about 7,500 light-years from Earth in the constellation Carina. Scientists thought a companion star in orbit around Eta Carinae might explain some of its strange properties, but researchers lacked direct evidence a companion star existed.

“Until now, Eta Carinae’s partner has evaded direct detection,” said Dr. Rosina Iping, a research scientist at Catholic University of America in Washington. “This discovery significantly advances our understanding of the enigmatic star.”

Evidence that Eta Carinae might be a double star system was inferred from a repeating pattern of changes in visual, X-ray, radio and infrared light over approximately 5.5 years. Astronomers thought a second star in a 5.5 year orbit around Eta Carinae might cause the repeated changes in its light. The strongest indirect evidence supporting the double star theory is that once every 5.5 years, the X-rays coming from the system disappear for about three months. Eta Carinae is too cool to generate X-rays, but it continuously blasts a flow of gas into space as a stellar wind at about 300 miles per second.

If its companion has a similar wind, their stellar winds would collide with enough force to generate the X-rays. This collision region must lie somewhere between the two stars.

As Eta Carinae moves in its orbit, it passes in front of the region where the winds collide, as viewed from Earth. When this occurs, Eta Carinae eclipses the X-rays once every 5.5 years, causing them to disappear. The last X-ray eclipse began on June 29, 2003. The 5.5 year orbit places the companion star only about 10 times farther from Eta Carinae than Earth is from the sun. Eta Carinae is too far away for telescopes to distinguish two stars in such a close orbit.

Another way to find evidence of a double-star system would be to detect the light of the second star, which in this case is much fainter than Eta Carinae. Several scientists searched for light from Eta Carinae’s companion using ground-based telescopes, but none succeeded. Because the companion is thought to be much hotter than Eta Carinae, astronomers reasoned it should be brighter at shorter wavelengths like ultraviolet light. However, it still escaped detection when it was searched for using the ultraviolet capabilities of the Hubble Space Telescope.

Iping and her collaborators used the satellite to detect the companion, because it can see even shorter ultraviolet wavelengths than Hubble. The team observed the far-ultraviolet light from Eta Carinae with the satellite on June 10, 17 and 27, 2003, right before the expected X-ray eclipse. While the far ultraviolet light from Eta Carinae was seen in the observations from June 10 and 17, it vanished on the 27, two days before the X-ray eclipse.

The disappearance of far ultraviolet light so close to the X-ray eclipse implies when Eta Carinae eclipsed the X-rays, it also eclipsed the companion star. The far-ultraviolet light observed prior to the eclipse was from the hotter companion, because Eta Carinae is too cool to emit much far-ultraviolet light.

“This far ultraviolet light comes directly from Eta Carinae’s companion star, the first direct evidence that it exists,” said Dr. George Sonneborn. He is Far Ultraviolet Spectroscopic Explorer Project Scientist at NASA’s Goddard Space Flight Center, Greenbelt, Md. “The companion star is much hotter than Eta Carinae, settling a long-standing mystery about this important star.”

This discovery will be published today in the Astrophysical Journal Letters. Authors include Iping, Sonneborn and Ted Gull of Goddard; Derck Massa of SGT Inc., Greenbelt, Md.; and John Hiller of the University of Pittsburgh. The project is a NASA Explorer mission developed in cooperation with the French and Canadian space agencies by Johns Hopkins University, Baltimore, University of Colorado, Boulder, and University of California, Berkeley. Goddard manages the program for NASA’s Science Mission Directorate. For images and information about the project on the Web, visit:

Original Source: NASA News Release

Black widow nebula. Image credit: NASA/Spitzer. Click to enlarge.
Unsuspecting prey be warned! Hiding in the darkest corner of the constellation Circinus is a gigantic black widow spider waiting for its next meal. For decades, this galactic creepy crawler has remained largely invisible, cunningly escaping visible-light detection. At last, it has finally been caught by NASA’s Spitzer Space Telescope’s dust-piercing, infrared eyes.

The spider is actually a star-forming cloud of gas and dust. In this Halloween interactive image comparison, an hourglass-shaped insignia, typically found on the underbelly of a black widow spider, can be seen faintly in the visible-light image from Digital Sky Survey (DSS). As Spitzer’s infrared image fades in, the veil of galactic dust shrouding the rest of the spider is lifted to reveal a poisonous widow.

In the Spitzer image, the two opposing bubbles that make up the black widow’s body are being formed in opposite directions by the powerful outflows from massive groups of forming stars. The baby stars can be seen inside the widow’s “stomach” where the two bubbles meet.

When individual stars form from molecular clouds of gas and dust they produce intense radiation and very strong particle winds. Both the radiation and the stellar winds blow the dust outward from the star creating a cavity or, bubble.

In the case of the Black Widow Nebula, astronomers suspect that a large cloud of gas and dust condensed to create multiple clusters of massive star formation. The combined winds from these large stars probably blew out bubbles into the direction of least resistance, forming a double-bubble.

Original Source: Spitzer News Release

Image credit: Derek Breit. Click to enlarge.
Findings of this nature are one of the many reasons why International Occultation Timing Association (IOTA) members pursue their craft. One of the notable and historic discoveries on a standard star by occultation means happened in 1819 when Antares’ companion star was observed. However, the name of the astronomy game is confirmation – and also filming and timing the northern limit event at differing locations were Walt Morgan and Ed Morana.

Contacting IOTA’s Dr. David Dunham, Breit forwarded his findings, contacted team members and started seeking an answer for two unusual seconds of video. According to Dunham’s response, “Almost 2 seconds with a distance of much more than a km; it’s unlikely that the Moon would be that smooth, it would have to be within about 5m or less for the brightness to remain faint and constant at that level so long. Especially since this apparently occurred at nearly every event, a faint, close companion, only 0.01″ to 0.02″ north of the primary, seems likely.”

And Morgan clarifies, “The disappearances and reappearances by upsilon Geminorum as it passed lunar peaks were usually slow transitions, that is, the star appeared to fade (or brighten) over a matter of several video frames. That was not considered unusual because of the fairly large angular diameter of the star. However, in some instances the magnitude 4.1 star did not seem to completely disappear on Breit’s record: a very faint point of light remained visible right at the lunar limb.”

But confirmation of such importance to the scientific community doesn’t stop there. Breit’s findings went out to all IOTA observers and the critical timing information provided them with the clues they needed. Also recording the event was Dr. Richard Nolthenius, whose answer was, “Derek’s right! I’ve just reduced my upsilon Gem graze video recording from last Friday. I used a PC164c on an 8″ f/10 operating at f/6.3, recorded on my Canon ZR45mc. And the conclusion is…. Derek’s camcorder is not going crazy! I fully confirm his observations and conclusions – this star is a very close double star.”

As they continue to work through the geometry and astrometric angles, Dr. Nolthenius offers the following information from his own recordings: “The second and 3rd D’s look especially like there is an 11th magnitude companion, and the final D most dramatic of all, with the initial fade happening in just 3 frames, followed by a definite but very faint 11th magnitude star left over for fully 1 second before finally disappearing.”

Although it might seem that in a sky filled with innumerable double stars that a revelation of this type would be of little significance, IOTA member – Dr. Michael Richmond – knew better: “I did a little searching to see if there was any other indication that upsilon Geminorum might be double. The Hipparcos observations indicate that it is slightly variable, with an amplitude of about 0.08 mag, but there is no indication of a period. The Astrophysics Data Service has a number of references which mention upsilon Geminorum. This star has been chosen to be a calibrator for optical interferometers; that is, people have decided that it’s a good star to use as a reference when doing high angular resolution measurements. There are two recent papers which list measurements of its angular size: Borde et al. (A&A 393, 183, 2002), which finds an angular diameter of 5.00 +/- 0.051 mas, and Richichi and Percheron (A&A 386, 492, 2002), which lists angular diameter of 5.23 +/- 0.31 mas. Given the Hipparcos parallax of 13.57 mas, this means that the star’s diameter is roughly 0.37 AU. The main star has spectral type listed as late K or early M giant, with V-band mag 4.08 and K-band mag 0.24. If this is a double star, with a companion of roughly mag 11, then it would be important to let other astronomers know: it would no longer be a really good calibration star.”

But, Dr. Richmond did not let his findings rest there and he continued to look for more precise information. Says Richmond, “I found that both of the catalogue entries were NOT based on direct measurements of angular size; instead, they were simply estimates, based on the observed brightness and the shape of the spectrum. In other words, they were basically fits to a blackbody with a given temperature. I was surprised to find such indirect evidence appearing in catalogues of angular size, for use as a calibrator for interferometers.”

Recognizing the importance of such a finding as opposed to known data definitely changes the way we perceive information. Astronomy is a continually upgrading science as Dr. Nolthenius notes: “For some 9th magnitude star, finding yet another double is one thing, but for such a bright star, being a standard for certain measurements should be checked, as you did. The star is apparently in that fall-through-the-cracks area of parameter space: a wide enough double to not make for noticeable periodicity in the radial velocity on a time scale of a few years – the period is likely in the 100+ year range, (although this is something I will calculate later) and yet impossibly difficult as a visual binary without using interferometry or lunar occultations.”

Of course, there is far more to this picture than just the discovery of undisclosed double star. By recording, timing, and observing both grazing and occultation events, IOTA is able to help determine proper movement, orbit and lunar limb features as well. As Dr. Nolthenius explains, “The absolute UT’s of the events will help in assessing the slope of the moon at the event points. However, the most convincing case for duplicity will be identifying significant periods of time of constant brightness at the very faint levels.” The diffraction of large stars aids astronomers in making more accurate calculations, “Perhaps there is a secondary that is of order 1 radius or less above the surface of upsilon Geminorum.” hypothesizes Nolthenius, “If such extended periods of very faint levels might be consistent with limb darkening which is very extended. As a K giant, I would not expect the limb darkening to be so extreme – normally limb darkening is more extreme the cooler the star, and late K is not all that cool.”

More confirmation was needed and the findings were sent to Dr. Mitsuru Soma of the National Astronomical Observatory of Japan. Says Soma, “From the comparison of your faint flash mentioned above and the short duration (0.7s) from R to D of the primary of Walter Morgan the companion’s separation from the primary is estimated to be about 0.04 arcsec, and this is consistent with the duration of your gradual R’s at 4:39:07 and at 4:40:21 (UT). The spectral type of ups Gem is K5III which is the same as Aldebaran according to the Hipparcos catalogue, so I assume that the actual radius of ups Gem is almost the same as Aldebaran. The angular radius of Aldebaran was estimated to be about 0.010 arcsec from lunar occultations.”

But confirmation means being very sure that there is no chance of this being a diffraction effect. As Dr. Soma explains, “The distance to ups Gem is 3.6 times the distance to Aldebaran (ups Gem’s parallax is 0.014 arcsec and Aldebaran’s parallax is 0.050 arcsec) so the angular radius of ups Gem should be about 0.003 arcsec, which is small so that I think the error arisen from the assumption that the star is a point source is almost negligible when we estimate the diffraction effects. Referring to this fact I think 0.04 arcsec I mentioned above is too large to be attributed to the diffraction effects.”

Confirmation continues on a deeper level when Dr. Michael Richmond plots the photometry of all three tapes of the Upsilon Geminorum event: “The thing I find very interesting and encouraging is that I see an asymmetry in these light curves.” says Richmond, “If this is true, then I think we can make a good case that there may be a faint companion to the primary star. The companion must be “ahead” of the primary, so that the moving limb of the moon first blocks (or reveals) the companion, before it blocks (or reveals) the primary.”

Dr. Mitusuru Soma also continued with his analysis and presented the papers at the Journees 2005 meeting in Warsaw on 2005 September 19-21. Based on available information says, “My conclusion about the position of the secondary of upsilon Geminorum relative to the primary is 0″.04 +/- 0″.01 in separation and 70deg +/- 20deg in PA.” Although these findings are preliminary, Soma will continue to review the data and clarify the results of all accumulative information.

Seeing double? The answer is quite probable. In the mean time IOTA members will continue to review of the data and further research the duplicity of upsilon Geminorum. There’s a whole big wide sky out there, and each time an observation of this type is made it adds more to our understanding. While speckle interferometry is cutting edge of double star detection – the occultation method can reveal far more. Contributions from dedicated members are what makes the International Occultation and Timing Association play an important role in today’s astronomy.

Says Breit, “It was a pretty darn good feeling when Dr Nolthenius wrote “Derek’s RIGHT!” When four PhD’s say I have found something special doing a hobby I taught myself from the age of six, that’s pretty good. Something to tell the grandkids… But my real thought was that I finally have a great video to show others and hopefully get them interested in observing these very dynamic and temporal events!” So what are the chances of IOTA members Derek Breit, Walt Morgan, Ed Morana and Michael Richmond making a contribution to the scientific community?

I’d say double.

Written by Tammy Plotner.

Our planet. Image credit: NASA/JPL. Click to enlarge.
New research allows geologists to estimate the time at which the Earth’s core separated from its rocky outer shell.

A paper in this week’s Nature [26 October 2005] shows how the problem can be resolved by considering the effect of a giant impact with the Earth.

Previous research, using two different types of radioactive ‘clocks’ (hafnium-tungsten and uranium-lead), appeared to give conflicting core formation times of about 35 and 80 million years, respectively, after the origin of the solar system.

The collision of a Mars-sized object with the Earth is thought to have contributed to the last ten percent of the Earth’s mass, as well as forming the Moon.
“The explanation may be that the hafnium-tungsten clock represents the initial phase of core formation, whereas the uranium-lead clock, that gives a younger age, has been reset by the upheaval introduced by the giant impact.”
Professor Bernie Wood

Professor Bernard Wood, who completed this research while at Bristol University, and Professor Alex Halliday from Oxford University, propose that the impact would have also changed the conditions of core formation.

They put forward a model that explains the discrepancy between the two isotope clocks if the effects of the oxidation state of the mantle are taken into account.

Professor Wood said: “The explanation may be that the hafnium-tungsten clock represents the initial phase of core formation, sometime before 35 million years after the origin of the solar system, whereas the uranium-lead clock, that gives a younger age of about 80 million years after the origin of the solar system, has been reset by the upheaval introduced by the giant impact.”

The impact could have produced an oxidation state under which a sulphur-rich metal formed – of which the core is now composed. This oxidation state would have readily allowed lead to dissolve, effectively resetting the uranium-lead clock and resulting in the younger age.

Original Source: University of Bristol News Release

Artist illustration of microscopic crystals surrounding a dusty disk. Image credit: NASA/JPL. Click to enlarge.
NASA’s Spitzer Space Telescope has spotted the very beginnings of what might become planets around the puniest of celestial orbs – brown dwarfs, or “failed stars.”

The telescope’s infrared eyes have for the first time detected clumps of microscopic dust grains and tiny crystals orbiting five brown dwarfs. These clumps and crystals are thought to collide and further lump together to eventually make planets. Similar materials are seen in planet-forming regions around stars and in comets, the remnants of our own solar system’s construction.

The findings provide evidence that brown dwarfs, despite being colder and dimmer than stars, undergo the same initial steps of the planet-building process.

“We are learning that the first stages of planet formation are more robust than previously believed,” said Dr. Daniel Apai, an astronomer at the University of Arizona, Tucson, and member of the NASA Astrobiology Institute’s Life and Planets Astrobiology Center. “Spitzer has given us the possibility to study how planets are built in widely different environments.”

The observations also imply that brown dwarfs might be good targets for future planet-hunting missions. Astronomers do not know if life could exist on planets around brown dwarfs.

Brown dwarfs differ from stars largely due to their mass. They lack the mass to ignite internally and shine brightly. However, they are believed to arise like stars, out of thick clouds of gas and dust that collapse under their own weight. And like stars, brown dwarfs develop disks of gas and dust that circle around them. Spitzer has observed many of these disks, which glow at infrared wavelengths.

Apai and his team used Spitzer to collect detailed information on the minerals that make up the dust disks of six young brown dwarfs located 520 light-years away, in the Chamaeleon constellation. The six objects range in mass from about 40 to 70 times that of Jupiter, and they are roughly 1 to 3 million years old.

The astronomers discovered that five of the six disks contain dust particles that have crystallized and are sticking together in what may be the early phases of planet assembling. They found relatively large grains and many small crystals of a mineral called olivine.

“We are seeing processed particles that are linking up and growing in size,” said Dr. Ilaria Pascucci, a co-author also of the University of Arizona. “This is exciting because we weren’t sure if the disks of such cool objects would behave the same way that stellar disks do.”

The team also noticed a flattening of the brown dwarfs’ disks, which is another sign that dust is gathering up into planets.

A paper on these findings appears online today in Science. Authors of the paper also include Drs. Jeroen Bouwman, Thomas Henning and Cornelis P. Dullemond of the Max Planck Institute for Astronomy, Germany; and Dr. Antonella Natta of the Osservatorio Astrofisico di Arcetri, Italy.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA’s Science Mission Directorate. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spitzer’s infrared spectrograph, which made the observations, was built by Cornell University, Ithaca, N.Y. Its development was led by Dr. Jim Houck of Cornell. The NASA Astrobiology Institute, founded in 1997, is a partnership between NASA, 16 major U.S. teams and six international consortia.

For artist concepts, graphics and more information about Spitzer, visit http://www.spitzer.caltech.edu/spitzer/ . For more information about the NASA Astrobiology Institute, visit http://nai.arc.nasa.gov/ . For more information about NASA and agency programs on the Web, visit http://www.nasa.gov/home/ .

Original Source: NASA/JPL News Release

Spiral Galaxy NGC 2403. Image credit: Subaru. Click to enlarge.
Subaru Telescope, using Suprime-Cam, took the clearest most complete image to date of the spiral galaxy NGC 2403. At a distance of 10 million light years, NGC 2403 is an Sc type galaxy, which has open spiral arms and a small nucleus. It is approximately half the mass of our own galaxy, the Milky Way, and has an abundance of neutral hydrogen gas. In the spiral arms we see active star formation regions in red, clusters of young blue stars called OB associations, and darker regions called dust lanes where light is blocked by gas and dust within the galaxy.

This is not the first time NGC 2403 has been studied. Edwin Hubble used NGC 2403 as evidence that more distant galaxies move more quickly away from us, now called Hubble’s Law. It was also used to develop the Tully-Fisher relation, which states that there is a relation between a galaxy’s rotational speed and its brightness. NGC 2403 has become an important standard galaxy when deciding the distances to other galaxies, as we recognize the vast expanse of space.

Larger galaxies are thought to have developed from the collision and merger of smaller galaxies. Mergers can leave enduring marks on a galaxy’s halo, the most extended and generally spherical component of a galaxy. There is evidence that relatively young stars exist in the halo of NGC 2403, hinting at a recent merger with another galaxy. Astronomers are now studying this image to see if the color and brightness of the stars in the halo of NGC 2403 will reveal conclusive evidence of past mergers.

Original Source: Subaru News Release

Giant mosaic of Andromeda made up of 11,000 images. Image credit: NASA/JPL. Click to enlarge.
NASA’s Spitzer Space Telescope has captured a stunning infrared view of Messier 31, the famous spiral galaxy also known as Andromeda.

Andromeda is the most-studied galaxy outside our own Milky Way, yet Spitzer’s sensitive infrared eyes have detected captivating new features, including bright, aging stars and a spiral arc in the center of the galaxy. The infrared image also reveals an off-centered ring of star formation and a hole in the galaxy’s spiral disk of arms. These asymmetrical features may have been caused by interactions with the several satellite galaxies that surround Andromeda.

“Occasionally small satellite galaxies run straight through bigger galaxies,” said Dr. Karl Gordon of the Steward Observatory, University of Arizona, Tucson, lead investigator of the new observation. “It appears a little galaxy punched a hole through Andromeda’s disk, much like a pebble breaks the surface of a pond.”

The new false-color Andromeda image is available at http://www.spitzer.caltech.edu/spitzer/ .

Approximately 2.5 million light-years away, Andromeda is the closest spiral galaxy and is the only one visible to the naked eye. Unlike our Milky Way galaxy, which we view from the inside, Andromeda is studied from the outside. Astronomers believe that Andromeda and the Milky Way will eventually merge together.

Spitzer detects dust heated by stars in the galaxy. Its multiband imaging photometer’s 24-micron detector recorded approximately 11,000 separate infrared snapshots over 18 hours to create the new comprehensive mosaic. This instrument’s resolution and sensitivity is a vast improvement over previous infrared technologies, enabling scientists to trace the spiral structures within Andromeda to an unprecedented level of detail.

“In contrast to the smooth appearance of Andromeda at optical wavelengths, the Spitzer image reveals a well-defined nuclear bulge and a system of spiral arms,” said Dr. Susan Stolovy, a co-investigator from the Spitzer Science Center at the California Institute of Technology, Pasadena.

The galaxy’s central bulge glows in the light emitted by warm dust from old, giant stars. Just outside the bulge, a system of inner spiral arms can be seen, and outside this, a well-known prominent ring of star formation.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology. The Jet Propulsion Laboratory is a division of Caltech.

Original Source: NASA/JPL News Release

Chandra image of Sgr A*. Image credit: Chandra. Click to enlarge.
NASA’s Chandra X-ray Observatory revealed a new generation of stars spawned by a super-massive black hole at the center of the Milky Way galaxy. This novel mode of star formation may solve several mysteries about these super-massive black holes that reside at the centers of nearly all galaxies.

“Massive black holes are usually known for violence and destruction,” said Sergei Nayakshin of the University of Leicester, United Kingdom. “So it’s remarkable this black hole helped create new stars, not just destroy them.”

Black holes have earned their fearsome reputation because any material, including stars, that falls within their “event horizon” is never seen again. These new results indicate immense disks of gas, orbiting many black holes at a safe distance from the event horizon, can help nurture the formation of new stars. This conclusion comes from new clues that could only be revealed in X-rays. Until the latest Chandra results, researchers have disagreed about the origin of a mysterious group of massive stars discovered by infrared astronomers.

The stars orbit less than a light year from the Milky Way’s central black hole, which is known as Sagittarius A* (Sgr A*). At such close distances to Sgr A*, the standard model for star forming gas clouds predicts they should have been ripped apart by tidal forces from the black hole. Two models, based on previous research, to explain this puzzle have been proposed. In the disk model, the gravity of a dense disk of gas around Sgr A* offsets the tidal forces and allows stars to form.

In the migration model, the stars formed in a cluster far away from the black hole and then migrated in to form the ring of massive stars. The migration scenario predicts about a million low mass, sun-like stars in and around the ring. In the disk model, the number of low mass stars could be much less.

Researchers used Chandra observations to compare the X-ray glow from the region around Sgr A* to the X-ray emission from thousands of young stars in the Orion Nebula star cluster. They found the Sgr A* star cluster contains only about 10,000 low mass stars, thereby ruling out the migration model. Because the galactic center is shrouded in dust and gas, it has not been possible to look for the low-mass stars in optical observations. X-ray data have allowed astronomers to penetrate the veil of gas and dust and look for these low mass stars.

This research, coauthored by Nayakshin and Rashid Sunyaev of the Max Plank Institute for Physics in Garching, Germany, will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society.

“In one of the most inhospitable places in our galaxy, stars have prevailed,” Nayakshin said. “It appears star formation is much more tenacious than we previously believed.” “We can say the stars around Sgr A* were not deposited there by some passing star cluster, rather they were born there,” Sunyaev said. “There have been theories that this was possible, but this is the first real evidence. Many scientists are going to be very surprised by these results.”

The research suggests the rules of star formation change when stars form in the disk surrounding a giant black hole. Because this environment is very different from typical star formation regions, there is a change in the proportion of stars that form. For example, there is a much higher percentage of massive stars in the disks around black holes.

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass. For more information about this research on the Web, visit:

Additional information and images are available at:

http://chandra.harvard.edu and http://chandra.nasa.gov

Original Source: Chandra News Release