- Hubble Finds Farthest, Oldest Galaxies Ever Seen
- Elusive Supermassive-Black-Hole Mergers Finally Found
- New Exoplanet Hunter Makes First 5 Discoveries
Posted: 05 Jan 2010 09:43 AM PST
By pushing the refurbished Hubble Space Telescope to its very limits as a cosmic time machine, astronomers have identified three galaxies that may hail from an era only a few hundred million years after the Big Bang. The faint galaxies may be the most distant starlit bodies known, each lying some 13.2 billion light-years from Earth.
Detecting galaxies at such a distance is at the very edge of what current technology can accomplish, comments Richard Ellis of Caltech, who was not part of the new study. It's uncharted territory, he says.
If the researchers are correct in the preliminary determination, then Hubble is seeing light that reveals the galaxies as they first appeared just 480 million years after the birth of the universe. (That light traveled for billions of years to reach Earth.) The radiation from such early galaxies played a crucial role, theorists believe, in reionizing the universe. That process breaks apart neutral atoms into electrons and ions, a process that enabled light from the first generation of stars to stream freely into space.
The astronomers caution that because the galaxies they found with Hubble are seen at only one wavelength, it's not certain that the bodies are extremely distant; they could just be red and faint. "We certainly don't have smoking gun evidence," says study coleader Rychard Bouwens of the University of California, Santa Cruz. "We just have tantalizing evidence that suggests we may be identifying a few [extremely distant] galaxies."
Bouwens and Garth Illingworth, also of UC Santa Cruz , along with several collaborators, posted their findings online December 23at the physics arXiv.org site (http://arxiv.org/abs/0912.4263). The team, like several others, went hunting for distant galaxies using Hubble's newly installed Wide Field Camera 3, which in August took a long look in infrared wavelengths at a patch of sky known as the Hubble Ultra Deep Field. Another Hubble camera had examined that field five years earlier in visible light, revealing many faint, faraway galaxies, but not the most remote galaxies, which can only be seen in infrared.
Ultraviolet and visible light emitted by the youthful stars in the earliest, most distant galaxies is shifted to much longer wavelengths — the infrared part of the spectrum — by the expansion of the universe. The more remote the galaxy, the greater the redshift.
In September, two teams, including Bouwens', reportedfinding galaxies with redshift values of seven to eight, corresponding to an era about 700 million years after the Big Bang. Now, the researchers estimate that another three galaxies imaged by the camera have a redshift of about 10, which if confirmed would be the largest redshift ever measured. Bouwens says that several tests, including observations with the infrared Spitzer Space Telescope, indicate that the galaxies they spotted are likely to be truly remote, reducing the possibility that his team is being fooled by intrinsically faint, infrared-emitting galaxies that lie much closer to Earth.
Other teams, notably a group that includes Rogier Windhorst of Arizona State University in Tempe and Haojing Yan of Ohio State University in Columbus, reporting earlier on arXiv.org (http://arxiv.org/abs/0910.0077), claimed to have found 20 galaxies at that same high redshiftusing the same data from the refurbished Hubble.
Garth and Illingworth note that most of the candidate distant galaxies identified by the Windhorst team lie near known, bright galaxies. They suggest that the team may have been confused by stray light from these bright galaxies. Other astronomers say it would be surprising if all 20 galaxies were from the same early era, since the Ultra Deep Field encompasses a narrow strip of sky. That would indicate that the early universe had a surprisingly high density of such galaxies.
Although the race is on to find more-convincing examples of distant galaxies, "redshift-10 galaxies are about the very edge that our current technology can push to," notes Yan. It's likely that none of the distant galaxy candidates can be confirmed until the launch of Hubble's powerful infrared successor, the James Webb Space Telescope, around 2014, astronomers agree.
Image: NASA/ESA /Z. Levay (STScI)
Posted: 05 Jan 2010 02:30 AM PST
WASHINGTON — The universe is one big dance party for black holes. New observations from the W.M. Keck Observatory in Hawaii and the Hubble Space Telescope found 33 merged galaxies in which pairs of supermassive black holes are "waltzing" around the galactic centers.
"Our result shows that such waltzing black holes are much more common than we previously knew," said Julie Comerford of the University of California, Berkeley. Comerford presented her results on January 4 at the winter meeting of the American Astronomical Society.
Finding pairs of black holes moving in a certain way can help estimate how often galaxy mergers occur in the universe. Observations have shown that nearly every galaxy has a supermassive black hole — a black hole with a mass of one million to one billion times that of the sun — at its center and that galaxies often collide and merge to create larger galaxies. Astronomers have expected to find many mid-merge galaxies by focusing on the two supermassive black holes, which should be orbiting each other in the middle. But so far, the dance floor has pretty much been empty.
"We expect the universe to be littered with these waltzing black holes," Comerford said. "But until recently, only a few had ever been found." Those missing black hole pairs posed problems for theories of how galaxies merge and grow.
Now, using two new observational techniques, Comerford and her colleagues have found 33 galaxies with dual supermassive black holes. The first technique found 32 black hole pairs in the DEEP2 Galaxy Redshift Survey conducted on the Keck II Telescope on Hawaii's Mauna Kea, by determining whether each black hole is moving toward or away from Earth.
Black holes are visible only when they can accrete gas and other material from the surrounding environment. Energy from the black hole heats the gas, lighting the gas up in visible wavelengths. When the black hole is moving away from Earth, the light from the accreted gas appears to be at a longer wavelength, or redshifted. When the black hole dances toward Earth, its light is blueshifted — meaning it has a shorter wavelength. The team identified waltzing pairs by looking for instances when one black hole was blueshifted and the other redshifted.
"It's kind of the disco ball that tells you where the party is, where the black holes are dancing," Comerford said.
The waltz is quick — both black holes are moving at velocities of about 200 kilometers per second. But the black holes are keeping "a chaste distance," Comerford said. They are separated on average by about 3,000 to 8,000 light-years, or one-eighth to one-third the distance from the sun to the center of the Milky Way.
For the population of galaxies Comerford and her colleagues observed, which were mostly gas-poor galaxies 4 billion to 7 billion light years from Earth, galaxy mergers occur three times every billion years, Comerford said.
The final black hole duo was found serendipitously in a Hubble image of a galaxy called COSMOS J100043.15+020637.2. The galaxy sports a tidal tail of stars, gas and dust, a sure sign of a recent galaxy merger.
"It's like a black eye, a sign that this galaxy has recently gone through a collision with another galaxy," Comerford said.
The galaxy also has two bright nuclei, each of which could be a supermassive black hole surrounded by glowing dust and gas. Follow-up observations with the Keck II Telescope showed the telltale velocity shifts of dancing black holes.
But the black holes might not be two waltzers. Instead, the data could point to one black hole that is fleeing the galaxy. When two black holes merge together, they produce gravitational waves that carry momentum away from the resulting larger black hole. Gravitational waves pointed mostly in one direction can "kick" the black hole in the opposite direction. Black holes could wander through their host galaxies, or, if the kick is large enough, leave the galaxy behind.
Observations of the same galaxy by Francesca Civano of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and colleagues suggest that the two bright sources are flying apart at a velocity of about 1,300 kilometers per second. Civano also presented her results at the American Astronomical Society meeting on January 4.
"For a merger, that is a bit high," Civano said. "But this number is completely normal for a gravitational wave kick."
"Whether this thing is a dual pair of waltzing black holes or an ejected black hole, this is definitely a merger," Comerford said. "It's just whether you're seeing it before the black holes merge [with each other] or after."
Posted: 04 Jan 2010 01:23 PM PST
The Kepler Space Telescope, a designated planet-hunting satellite, has found its first five planets, among them an odd, massive world only as dense as styrofoam.
The number of planets now known outside the solar system has risen to over 400, but none is yet Earth-like enough to harbor life. Right now, Kepler can only detect large planets orbiting close to their stars, which means that these first planets are too hot to hold liquid water, a requirement for life as we know it.
But over the next year, the mission's scientists will be honing in on ever more life-friendly places.
"We expected Jupiter-size planets in short orbits to be the first planets Kepler could detect," said Jon Morse, director of the Astrophysics Division at NASA in a release. "It's only a matter of time before more Kepler observations lead to smaller planets with longer period orbits, coming closer and closer to the discovery of the first Earth analog."
Kepler is pointed at a single field of stars in the constellation Cygnus. By watching the same stars over time, the mission can detect the periodic dimming of those stars,a possibleindication that a planet has passed in front of the star. Finding an Earth-like planet will probably take quite a while, though, because if it has an Earth-like orbit, it will take around a year to cross in front of its star just one time.
The current set of Kepler planets are not much likeours at all. The smallest is 0.4 times the size of Jupiter, while the largest is 1.5 times the largest planet in our solar system. They are all very hot, too, running between 2,200 and 2,900 degrees Fahrenheit. They have been given the catchy names Kepler 4b, Kepler 5b, Kepler 6b, and Kepler 7b. (Kepler 1b-3b were assigned to previously known exoplanets in the telescope's field of view.)
Still, the planet detections show that Kepler is in great working order as it monitors its sample of the sky. The precision of the instrument has astounded scientists since its first light.
"This exquisite data is just the tip of the iceberg," MIT astronomer Sara Seager said back then. "We're going to see a new world of exoplanet exploration where discoveries will come much more rapidly than they've come in the last 10 years."
The mission, championed by Bill Borucki, a NASA extrasolar planet specialist, for more than a decade, looks like it will be capableof completing all of its scientific goals. That means it's just a matter of time before we find an Earth twin or two out there in the light-years beyond.
Image: NASA exoplanet rendering.
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