A mysterious flash of light from somewhere near or far in the universe is still keeping astronomers in the dark long after it was first detected by NASA's Hubble Space Telescope in 2006. It might represent an entirely new class of stellar phenomena that has previously gone undetected in the universe, say researchers.

Astronomers commonly observe intense flashes of light from a variety of stellar explosions and outbursts, such as novae and supernovae. Hubble discovered the cosmic flash on February 21, 2006. It steadily rose in brightness for 100 days, and then dimmed back to oblivion after another 100 days.

The rise and fall in brightness has a signature that simply has never been recorded for any other type of celestial event. Supernovae peak after no more than 70 days, and gravitational lensing events are much shorter. Therefore, this observation defies a simple explanation, reports Kyle Barbary of the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, Calif. He is describing the bizarre Hubble observation at the 213th meeting of the American Astronomical Society in Long Beach, Calif. "We have never seen anything like it," he concludes.

The spectral fingerprints of light coming from the object, cataloged as SCP 06F6, also have eluded identification as being due to any specific element. One guess is that the features are redshifted molecular carbon absorption lines in a star roughly one billion light-years away.

But searches through various astronomical survey catalogs for the source of the light have not uncovered any evidence for a star or galaxy at the location of the flash. The Supernova Cosmology Project at LBNL discovered it serendipitously in a search for supernovae.

Hubble was aimed at a cluster of galaxies 8 billion light-years away in the spring constellation Bootes. But the mystery object could be anywhere in between, even in the halo of our own Milky Way galaxy.

Papers published by other researchers since the event was reported in June 2006, have suggested a bizarre zoo of possibilities: the core collapse and explosion of a carbon rich star, a collision between a white dwarf and an asteroid, or the collision of a white dwarf with a black hole.

But Barbary does not believe that any model offered so far fully explains the observations. "I don't think we really know what the discovery means until we can observe similar objects in the future."

All-sky surveys for variable phenomena, such as those to be conducted with the planned Large Synoptic Survey Telescope, may ultimately find similar transient events in the universe.

Brown dwarfs, objects that are less massive than stars but larger than planets, just got more elusive, based on a study of 233 nearby multiple-star systems by NASA's Hubble Space Telescope. Hubble found only two brown dwarfs as companions to normal stars. This means the so-called "brown dwarf desert" (the absence of brown dwarfs around solar-type stars) extends to the smallest stars in the universe.

Sergio Dieterich of Georgia State University in Atlanta and team leader of the study is reporting the results today at the 213th meeting of the American Astronomical Society (AAS) in Long Beach, Calif.

"We still did not find brown dwarfs around small red stars whose mass is only slightly above the hydrogen burning limit. Especially when we consider the fact that brown dwarfs binaries do exist, the fact that there are very few binaries whose components lie on different sides of the hydrogen burning limit is significant," says Dieterich.

The 233 stars surveyed are part of the RECONS (Research Consortium on Nearby Stars) survey meant to understand the nature of the sun's nearest stellar neighbors, both individually and as a population. The current primary goals are to discover and characterize "missing" members of the sample of stars within 32.6 light-years (10 parsecs) of Earth.

RECONS searches for nearby stars through analyzing existing all-sky surveys, combined with observations by a variety of telescopes in both hemispheres. A total of 12 brown dwarfs are currently known within 32.6 light-years of Earth, as compared to 239 red dwarf stars (stars that are largely 20 percent the mass of our sun and are roughly half its diameter and temperature).

In fact, the number of known brown dwarfs is close to that of known extrasolar planets. However, the number of exoplanets known in this region so far is very likely only a lower limit as smaller-mass exoplanets are not within our capability of detection at present.

The Hubble survey, taken with Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS), provides strong statistics pointing to the fact that brown dwarfs do not exist around even the least massive stars. "If mass ratio was the driving factor we would expect to find more brown dwarfs around small red stars than around solar type stars," says Dieterich.

These results are complementary to another study also being reported at the AAS meeting by Micaela Stumpf of the Max-Planck-Institute for Astronomy in Heidelberg, Germany. The results imply that brown dwarfs tend to hang out with their own kind.

Nearly ten years' worth of NICMOS observations, combined with recent ground-based adaptive optics results, have provided a first estimate of the orbit of the double brown dwarf system Kelu-1 AB. The eccentric orbit is tilted nearly edge-on to Earth and the dwarfs complete an orbit every 38 years.

Based on the orbital dynamics, the total mass of the system is estimated to be 184 Jupiter masses. But, based on spectroscopic and photometric measurements, the two brown dwarfs are no larger than 61 and 50 Jupiter masses, respectively (a star is no smaller than 75 Jupiter masses). Stumpf is reporting that there may in fact be a third member of the system to account for the "missing mass." This would make it potentially the first-ever confirmed triple brown dwarf system.

All-sky surveys planned for the next decade, with advanced telescopes like the Large Synoptic Survey Telescope, promise to ultimately solve the puzzle of the "brown dwarf desert" by doing deep infrared searches for the underlying brown dwarf population.

Credit for Hubble image: NASA, ESA, and Q.D. Wang (University of Massachusetts, Amherst) Credit for Spitzer image: NASA, Jet Propulsion Laboratory, and S. Stolovy (Spitzer Science Center/Caltech)

This composite color infrared image of the center of our Milky Way galaxy reveals a new population of massive stars and new details in complex structures in the hot ionized gas swirling around the central 300 light-years. This sweeping panorama is the sharpest infrared picture ever made of the Galactic core. It offers a nearby laboratory for how massive stars form and influence their environment in the often violent nuclear regions of other galaxies.

This view combines the sharp imaging of the Hubble Space Telescope's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) with color imagery from a previous Spitzer Space Telescope survey done with its Infrared Astronomy Camera (IRAC). The Galactic core is obscured in visible light by intervening dust clouds, but infrared light penetrates the dust.

The spatial resolution of the NICMOS image corresponds to 0.025 light-years at the distance of the Galactic core of 26,000 light-years. Hubble reveals details in objects as small as 20 times the size of our own solar system.

The NICMOS mosaic image represents the largest piece of sky ever mapped for one NICMOS observing program. It was combined with a full-color Spitzer image to yield a color composite of the nuclear region. The picture measures 300 x 115 light-years. Outside the boundary of the NICMOS survey, the IRAC exposures (which are 1/10th as sharp) can be seen at wavelengths of 3.6 microns (shown as blue), 4.5 microns (shown as green), 5.8 microns (shown as orange), and 8.0 microns (shown as red).

The new NICMOS data show the glow from ionized hydrogen gas as well as a multitude of stars. Hubble reveals an important population of stars with strong stellar winds, signified by excess emission from ionized gas at one infrared wavelength (1.87 microns) compared to another slightly different wavelength (1.90 microns).

NICMOS shows a large number of these massive stars distributed throughout the region. A new finding is that astronomers now see that the massive stars are not confined to one of the three known clusters of massive stars in the Galactic Center, known as the Central cluster, the Arches cluster, and the Quintuplet cluster. These three clusters are easily seen as tight concentrations of bright, massive stars in the NICMOS image. The distributed stars may have formed in isolation, or they may have originated in clusters that have been disrupted by strong gravitational tidal forces.

The winds and radiation from these stars form the complex structures seen in the core, and in some cases, they may be triggering new generations of stars. At upper left, large arcs of ionized gas are resolved into arrays of intriguingly organized linear filaments indicating perhaps a critical role of the influence of locally strong magnetic fields.

The lower left region shows pillars of gas sculpted by winds from hot massive stars in the Quintuplet cluster. At the center of the image, ionized gas surrounding the supermassive black hole at the center of the galaxy is confined to a bright spiral embedded within a circum-nuclear dusty inner-tube-shaped torus.

The NICMOS mosaic required 144 Hubble orbits to make 2,304 science exposures. It was taken between February 22 and June 5, 2008.

This artist's conception of the Milky Way shows the four-arm spiral structure confirmed by recent VLBA distance measurements (shown by green and blue dots). The data show that the Milky Way is spinning faster than previously believed. Our galaxy therefore is more massive than astronomers thought, matching Andromeda's heft. Red dots mark the galactic center and the location of our solar system. Credit: Robert Hurt, IPAC; Mark Reid, CfA, NRAO/AUI/NSF

Fasten your seat belts -- we're faster, heavier, and more likely to collide than we thought. Astronomers making high-precision measurements of the Milky Way say our Galaxy is rotating about 100,000 miles per hour faster than previously understood.

That increase in speed, said Mark Reid of the Harvard-Smithsonian Center for Astrophysics, increases the Milky Way's mass by 50 percent, bringing it even with the Andromeda Galaxy. "No longer will we think of the Milky Way as the little sister of the Andromeda Galaxy in our Local Group family."

The larger mass, in turn, means a greater gravitational pull that increases the likelihood of collisions with the Andromeda galaxy or smaller nearby galaxies.

Our solar system is about 28,000 light-years from the Milky Way’s center. At that distance, the new observations indicate, we’re moving at about 600,000 miles per hour in our Galactic orbit, up from the previous estimate of 500,000 miles per hour.

The scientists are using the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope to remake the map of the Milky Way. Taking advantage of the VLBA’s unparalleled ability to make extremely detailed images, the team is conducting a long-term program to measure distances and motions in our Galaxy. They reported their results at the American Astronomical Society’s meeting in Long Beach, California.

The scientists observed regions of prolific star formation across the Galaxy. In areas within these regions, gas molecules are strengthening naturally-occurring radio emission in the same way that lasers strengthen light beams. These areas, called cosmic masers, serve as bright landmarks for the sharp radio vision of the VLBA. By observing these regions repeatedly at times when the Earth is at opposite sides of its orbit around the Sun, the astronomers can measure the slight apparent shift of the object’s position against the background of more distant objects.

“The new VLBA observations of the Milky Way are producing highly-accurate direct measurements of distances and motions,” said Karl Menten of the Max Planck Institute for Radio Astronomy in Germany, a member of the team. “These measurements use the traditional surveyor’s method of triangulation and do not depend on any assumptions based on other properties, such as brightness, unlike earlier studies.”

The astronomers found that their direct distance measurements differed from earlier, indirect measurements, sometimes by as much as a factor of two. The star-forming regions harboring the cosmic masers “define the spiral arms of the Galaxy,” Reid explained. Measuring the distances to these regions thus provides a yardstick for mapping the Galaxy’s spiral structure.

“These direct measurements are revising our understanding of the structure and motions of our Galaxy,” Menten said. "Because we’re inside it, it’s difficult for us to determine the Milky Way’s structure. For other galaxies, we can simply look at them and see their structure, but we can’t do this to get an overall image of the Milky Way. We have to deduce its structure by measuring and mapping,” he added.

The VLBA can fix positions in the sky so accurately that the actual motion of the objects can be detected as they orbit the Milky Way’s center. Adding in measurements of motion along the line of sight, determined from shifts in the frequency of the masers’ radio emission, the astronomers are able to determine the full 3-dimensional motions of the star-forming regions. Using this information, Reid reported that “most star-forming regions do not follow a circular path as they orbit the Galaxy; instead we find them moving more slowly than other regions and on elliptical, not circular, orbits.”

The researchers attribute this to what they call spiral density-wave shocks, which can take gas in a circular orbit, compress it to form stars, and cause it to go into a new, elliptical orbit. This, they explained, helps to reinforce the spiral structure.

Reid and his colleagues found other surprises, too. Measuring the distances to multiple regions in a single spiral arm allowed them to calculate the angle of the arm. “These measurements,” Reid said, “indicate that our Galaxy probably has four, not two, spiral arms of gas and dust that are forming stars.” Recent surveys by NASA’s Spitzer Space Telescope suggest that older stars reside mostly in two spiral arms, raising a question of why the older stars don't appear in all the arms. Answering that question, the astronomers say, will require more measurements and a deeper understanding of how the Galaxy works.

The VLBA, a system of 10 radio-telescope antennas stretching from Hawaii to New England and the Caribbean, provides the best ability to see the finest detail, called resolving power, of any astronomical tool in the world. The VLBA can routinely produce images hundreds of times more detailed than those produced by the Hubble Space Telescope. The VLBA’s tremendous resolving power, equal to being able to read a newspaper in Los Angeles from the distance of New York, is what permits the astronomers to make precise distance determinations.

This release was issued jointly with the National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

The planet Jupiter gained weight in a hurry during its infancy. It had to, since the material from which it formed probably disappeared in just a few million years, according to a new study of planet formation around young stars.

Smithsonian astronomers examined the 5 million-year-old star cluster NGC 2362 with NASA's Spitzer Space Telescope, which can detect the signatures of actively forming planets in infrared light. They found that all stars with the mass of the Sun or greater have lost their protoplanetary (planet-forming) disks. Only a few stars less massive than the Sun retain their protoplanetary disks. These disks provide the raw material for forming gas giants like Jupiter. Therefore, gas giants have to form in less than 5 million years or they probably won't form at all.

“Even though astronomers have detected hundreds of Jupiter-mass planets around other stars, our results suggest that such planets must form extremely fast. Whatever process is responsible for forming Jupiters has to be incredibly efficient,” said lead researcher Thayne Currie of the Harvard-Smithsonian Center for Astrophysics. Currie presented the team’s findings at a meeting of the American Astronomical Society in Long Beach, Calif.

Even though nearly all gas giant-forming disks in NGC 2362 have disappeared, several stars in the cluster have “debris disks,” which indicates that smaller rocky or icy bodies such as Earth, Mars, or Pluto may still be forming.

“The Earth got going sooner, but Jupiter finished first, thanks to a big growth spurt,” explained co-author Scott Kenyon.

Kenyon added that while Earth took about 20 to 30 million years to reach its final mass, Jupiter was fully grown in only 2 to 3 million years.

Previous studies indicated that protoplanetary disks disappear within 10 million years. The new findings put even tighter constraints on the time available to create gas giant planets around stars of various masses.

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, also in Pasadena. Caltech manages JPL for NASA.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

About this image: This artist's concept shows young, blue stars encircling a supermassive black hole at the core of a spiral galaxy like the Milky Way. The background stars are the typical older, redder population of stars that inhabit the cores of most galaxies (including our own). CfA astronomers caught two stars in the act of forming within a few light-years of the Milky Way's center. Their find demonstrates that stars can form at our galaxy's core despite the powerful gravitational tides generated by the black hole. Credit: NASA, ESA, and A. Schaller (for STScI)

The center of the Milky Way presents astronomers with a paradox: it holds young stars, but no one is sure how those stars got there. The galactic center is wracked with powerful gravitational tides stirred by a 4 million solar-mass black hole. Those tides should rip apart molecular clouds that act as stellar nurseries, preventing stars from forming in place. Yet the alternative – stars falling inward after forming elsewhere – should be a rare occurrence.

Using the Very Large Array of radio telescopes, astronomers from the Harvard-Smithsonian Center for Astrophysics and the Max Planck Institute for Radio Astronomy have identified two protostars located only a few light-years from the galactic center. Their discovery shows that stars can, in fact, form very close to the Milky Way’s central black hole.

“We literally caught these stars in the act of forming,” said Smithsonian astronomer Elizabeth Humphreys. She presented the finding today at a meeting of the American Astronomical Society in Long Beach, Calif.

The center of the Milky Way is a mysterious region hidden behind intervening dust and gas, making it hard to study. Visible light doesn’t make it out, leaving astronomers no choice but to use other wavelengths like infrared and radio, which can penetrate dust more easily.

Humphreys and her colleagues searched for water masers—radio signals that serve as signposts for protostars still embedded in their birth cocoons. They found two protostars located seven and 10 light-years from the galactic center. Combined with one previously identified protostar, the three examples show that star formation is taking place near the Milky Way’s core.

Their finding suggests that molecular gas at the center of our galaxy must be denser than previously believed. A higher density would make it easier for a molecular cloud’s self-gravity to overcome tides from the black hole, allowing it to not only hold together but also collapse and form new stars.

The discovery of these protostars corroborates recent theoretical work, in which a supercomputer simulation produced star formation within a few light-years of the Milky Way’s central black hole.

“We don’t understand the environment at the galactic center very well yet,” Humphreys said. “By combining observational studies like ours with theoretical work, we hope to get a better handle on what’s happening at our galaxy’s core. Then, we can extrapolate to more distant galaxies.”

Humphreys’ co-authors are Mark Reid (Harvard-Smithsonian Center for Astrophysics) and Karl Menten (Max Planck Institute for Radio Astronomy).

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.