NASA/JPL NEWS RELEASE
Posted: January 14, 2008NASA's Spitzer Space Telescope has detected plump black holes where least expected -- skinny galaxies.
Like people, galaxies come in different shapes and sizes. There are thin spirals both with and without central bulges of stars, and more rotund ellipticals that are themselves like giant bulges. Scientists have long held that all galaxies except the slender, bulgeless spirals harbor supermassive black holes at their cores. Furthermore, bulges were thought to be required for black holes to grow.
This artist's concept illustrates the two types of spiral galaxies that populate our universe: those with plump middles, or central bulges (upper left), and those lacking the bulge (foreground). Credit: NASA/JPL-Caltech
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The new Spitzer observations throw this theory into question. The infrared telescope surveyed 32 flat and bulgeless galaxies and detected monstrous black holes lurking in the bellies of seven of them. The results imply that galaxy bulges are not necessary for black hole growth; instead, a mysterious invisible substance in galaxies called dark matter could play a role.
"This finding challenges the current paradigm. The fact that galaxies without bulges have black holes means that the bulges cannot be the determining factor, " said Shobita Satyapal of the George Mason University, Fairfax, Va. "It's possible that the dark matter that fills the halos around galaxies plays an important role in the early development of supermassive black holes."
Satyapal presented the findings at the 211th meeting of the American Astronomical Society in Austin, Texas. A study from Satyapal and her team will be published in the April 10 issue of the Astrophysical Journal.
Our own Milky Way is an example of a spiral galaxy with a bulge; from the side, it would look like a plane seen head-on, with its wings out to the side. Its black hole, though dormant and not actively "feeding," is several million times the mass of our sun.
Previous observations had suggested that bulges and black holes flourished together like symbiotic species. For instance, supermassive black holes are almost always about 0.2 percent the mass of their galaxies' bulges. In other words, the more massive the bulge, the more massive the black hole. Said Satyapal, "Scientists reasoned that somehow the formation and growth of galaxy bulges and their central black holes are intimately connected."
But a wrinkle appeared in this theory in 2003, when astronomers at the University of California, Berkeley, and Observatories of the Carnegie Institution of Washington, Pasadena, Calif., discovered a relatively "lightweight" supermassive black hole in a galaxy lacking a bulge. Then, earlier this year, Satyapal and her team uncovered a second supermassive black hole in a similarly svelte galaxy.
In the latest study, Satyapal and her colleagues report the discovery of six more hefty black holes in thin galaxies with minimal bulges, further weakening the "bulge-black hole" theory. Why hadn't anybody seen these black holes before? According to the scientists, bulgeless galaxies tend to be very dusty, letting little visible light escape. But infrared light can penetrate dust, so the team was able to use Spitzer's infrared spectrograph to reveal the "fingerprints" of active black holes lurking in galaxies millions of light years away.
"A feeding black hole spits out high-energy light that ionizes much of the gas in the core of the galaxy," said Satyapal. "In this case, Spitzer identified the unique fingerprint of highly ionized neon -- only a feeding black hole has the energy needed to excite neon to this state." The precise masses of the newfound black holes are unknown.
If bulges aren't necessary ingredients for baking up supermassive black holes, then perhaps dark matter is. Dark matter is the enigmatic substance that permeates galaxies and their surrounding halos, accounting for up to 90 percent of a galaxy's mass. So-called normal matter makes up stars, planets, living creatures and everything we see around us, whereas dark matter can't be seen. Only its gravitational effects can be felt. According to Satyapal, dark matter might somehow determine the mass of a black hole early on in the development of a galaxy.
"Maybe the bulge was just serving as a proxy for the dark matter mass -- the real determining factor behind the existence and mass of a black hole in a galaxy's center," said Satyapal.
Other authors of this study include: D. Vega of the George Mason University; R.P. Dudik of the George Mason University and NASA Goddard Space Flight Center, Greenbelt, Md.; N.P. Abel of the University of Cincinnati, Ohio; and Tim Heckman of the Johns Hopkins University, Baltimore, Md.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope 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. Spitzer's infrared spectrograph was built by Cornell University, Ithaca, N.Y. Its development was led by Jim Houck of Cornell.
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New research shows that if our planet had been any smaller, there might not be anything living on it. Provided by Harvard-Smithsonian CfA A super-Earth like the one in this artist's conception can grow twice as large as Earth with up to 10 times the mass. Super-Earths are likely to be more life-friendly than our world because they would be more geologically active. David A. Aguilar (Harvard-Smithsonian CfA) [View Larger Image] January 9, 2008
Our planet is changing before our eyes, and as a result, many species are living on the edge. Yet Earth has been on the edge of habitability from the beginning. New work by astronomers at the Harvard-Smithsonian Center for Astrophysics shows that if Earth had been slightly smaller and less massive, it would not have plate tectonics, the forces that move continents and build mountains. And without plate tectonics, life might never have gained a foothold on our world.
"Plate tectonics are essential to life as we know it," says Diana Valencia of Harvard University. "Our calculations show that bigger is better when it comes to the habitability of rocky planets."
This research was the subject of a press conference at the 211th meeting of the American Astronomical Society.
Plate tectonics involve the movement of huge chunks, or plates, of a planet's surface. Plates spread apart from each other, slide under one another, and even crash into each other, lifting gigantic mountain ranges like the Himalayas. Plate tectonics are powered by magma boiling beneath the surface, much like a bubbling pot of chocolate. The chocolate on top cools and forms a skin or crust, just as magma cools to form the planet's crust.
Plate tectonics are crucial to a planet's habitability because they enable complex chemistry and recycle substances like carbon dioxide, which acts as a thermostat and keeps Earth balmy. Carbon dioxide that was locked into rocks is released when those rocks melt, returning to the atmosphere from volcanos and oceanic ridges.
"Recycling is important even on a planetary scale," Valencia explains.
Valencia and her colleagues, Richard O'Connell and Dimitar Sasselov (Harvard University), examined the extremes to determine whether plate tectonics would be more or less likely on different-sized rocky worlds. In particular, they studied so-called "super-Earths," planets more than twice the size of Earth and up to 10 times as massive. (Any larger, and the planet would gather gas as it forms, becoming like Neptune or even Jupiter.)
The team found that super-Earths would be more geologically active than our planet, experiencing more vigorous plate tectonics due to thinner plates under more stress. Earth itself was found to be a borderline case, not surprisingly since the slightly smaller planet Venus is tectonically inactive.
"It might not be a coincidence that Earth is the largest rocky planet in our solar system, and also the only one with life," says Valencia.
Exoplanet searches have turned up five super-Earths already, although none have life-friendly temperatures. If super-Earths are as common as observations suggest, then it is inevitable that some will enjoy Earth-like orbits, making them excellent havens for life.
"There are not only more potentially habitable planets, but MANY more," states Sasselov, who is director of the Harvard Origins of Life Initiative.
In fact, a super-Earth could prove to be a popular vacation destination to our far-future descendants. Volcanic "rings of fire" could span the globe while the equivalent of Yellowstone Park would bubble with hot springs and burst with hundreds of geysers. Even better, an Earth-like atmosphere would be possible, while the surface gravity would be up to three times that of Earth on the biggest super-Earths.
"If a human were to visit a super-Earth, they might experience a bit more back pain, but it would be worth it to visit such a great tourist spot," Sasselov suggests with a laugh.
He added that although a super-Earth would be twice the size of our home planet, it would have similar geography. Rapid plate tectonics would provide less time for mountains and ocean trenches to form before the surface was recycled, yielding mountains no taller and trenches no deeper than those on Earth. Even the weather might be comparable for a world in an Earth-like orbit.
"The landscape would be familiar. A super-Earth would feel very much like home," says Sasselov. |
Finding three galaxies lined up one behind another is less likely than winning two consecutive bets on the same number in roulette. So when astronomer Tommaso Treu (University of California, Santa Barbara) and his colleagues found such a galaxy trio, they knew they'd hit the cosmic jackpot.  This Hubble image of the obscure galaxy SDSS J0946+1006 in Leo shows it encircled by two concentric rings. These are distorted images of background galaxies whose light was bent as it passed J0946 en route to Earth. In the right-hand panel, which is about 5 arcseconds wide, the foreground galaxy has been subtracted to show the rings better. NASA / ESA / R. Gavazzi & T. Treu (UCSB) At the American Astronomical Society meeting in Austin, Texas, Treu unveiled the first-ever image of a double Einstein ring. It shows an obscure galaxy in Leo, designated SDSS J0946+1006 for its coordinates in the Sloan Digital Sky Survey, encircled by two concentric glowing rings. These aren't part of J0946 itself, but are the strongly distorted images of more distant galaxies strung out behind it like beads on a string. This is a spectacular example of a phenomenon called gravitational lensing. It's caused by the distortion of space-time by massive objects. While formulating his general theory of relativity, Albert Einstein realized that because of this warping, light won't always travel across the universe in straight lines. For example, if one galaxy lies almost directly behind another as seen from Earth, light from the more distant one will bend around the foreground galaxy and form multiple images — or, in the case of near-perfect alignment, an Einstein ring. Astronomers have found nearly 50 examples to date, most of them in SDSS images. When Treu's team first looked at the ring around J0946, they thought it was like all the others. But when they shot a close-up with the Hubble Space Telescope, they discovered a broken second ring outside the first. "When I first saw it," recalls Treu, "I said, 'Wow, this is insane!' I could not believe it." Treu and his colleagues were looking for Einstein rings because they can be used to map the distribution of mass in the universe — especially the unseen dark matter that seems to be many times more plentiful than the ordinary stuff that makes up the visible parts of galaxies. It works this way: from the distances of the galaxies and the shapes and brightnesses of the mirages, you can determine the amount and arrangement of mass in the foreground object (the "lens") needed to produce what you see. With two rings rather than just one, you can map the mass in two galaxies: the lensing one and the next one out, whose light is stretched to form the inner ring. In the double-ring system in Leo, the lensing (foreground) galaxy is about 2 billion light-years away, while the lensed (background) objects are 6 and 11 billion light-years distant. According to Treu, this means that J0946 has the mass distribution of a large spiral galaxy surrounded by a giant halo of dark matter — not unlike our own Milky Way. The middle galaxy is a dwarf with a mass of only a billion Suns, and it's now the most distant dwarf galaxy whose mass has ever been measured. For more information, see the press releases at the Space Telescope Science Institute and the European Space Agency's Hubble Information Centre. Posted by: Visite:
This newfound short GRB is the oldest ever discovered. Provided by the Goddard Space Flight Center Nobody knows how the short gamma-ray burst GRB 070714B was triggered, but a leading possibility is the inspiral and merger of two neutron stars, depicted in this artist rendition. NASA/Dana Berry [View Larger Image] January 9, 2008
Using the powerful one-two combo of NASA's Swift satellite and the Gemini Observatory, astronomers have detected a mysterious type of cosmic explosion farther back in time than ever before. The explosion, known as a short gamma-ray burst (GRB), took place 7.4 billion years ago, more than halfway back to the Big Bang.
"This discovery dramatically moves back the time at which we know short GRBs were exploding. The short burst is almost twice as far as the previous confirmed record holder," says John Graham of the Johns Hopkins University, in Baltimore, Maryland. Graham presented his group's discovery on Tuesday in a poster at the American Astronomical Society's 2008 winter meeting in Austin, Texas.
GRBs are among the most powerful explosions in the universe, releasing enormous amounts of energy in the form of X-rays and gamma rays. Most bursts fall in one of two categories: long bursts and short bursts, depending on whether they last longer or shorter than 3 seconds. Astronomers think that long GRBs are triggered by the collapse and explosion of massive stars. In contrast, a variety of mechanisms have been proposed for short bursts. The most popular model says that most short GRBs occur when two neutron stars smash into each other and collapse into a black hole, ejecting energy in two counterflowing beams.
The record-setting short burst is known as GRB 070714B, since it was the second GRB detected on July 14, 2007. Swift discovered the GRB in the constellation Taurus. The burst's high energy and 3-second duration firmly place it in the short GRB category. Rapid follow-up observations with the 2-meter Liverpool Telescope and the 4-meter William Herschel Telescope found an optical afterglow in the same location as the burst, which allowed astronomers to identify the GRB's host galaxy. | These illustrations show the view from afar. In the third image, we see two jets shooting away from the collision site. These jets are where the gamma rays are emitted. NASA/Dana Berry [View Larger Image] Next, Graham and his colleagues, Andrew Fruchter of the Space Telescope Science Institute, in Baltimore, and Andrew Levan of the University of Warwick, U.K., trained the 8-meter Gemini North Telescope in Hawaii on the galaxy. It revealed that the host galaxy has a spectral line from ionized oxygen. The amount that line was shifted toward the red end of the spectrum yields a redshift of 0.92. A redshift of 0.92 translates to a distance of 7.4 billion light-years, meaning the explosion occurred 7.4 billion years ago.
"The fact that this short burst is so far away means this subclass has a broad range of distances, although they still tend to be closer on average than long GRBs," says Swift lead scientist Neil Gehrels of NASA's Goddard Space Flight Center.
Gehrels adds that GRB 070714B's energy is about 100 times higher than average for short bursts, and is more similar to the typical energy of a long GRB. "It is unclear whether another mechanism is needed to explain this explosion, such as a neutron star-black hole merger. Or it could be that there are a wide range of energies for neutron star-neutron star mergers, but that seems unlikely."
Another possibility is that GRB 070714B concentrated its energy in two very narrow beams, and one of the beams happened to be aimed directly at Earth. This would make the burst seem more powerful than it really was. Perhaps most short GRBs eject their energy in wider and less-concentrated beams.
"We now have a good idea of the type of star that produces the brighter long bursts. But how short bursts are formed remains a mystery," says Fruchter. |
Solar Cycle 24 is officially here, say the professional sunwatchers at NOAA's Space Weather Prediction Center. The start of a new 11-year-long activity cycle was confirmed by January 3rd appearance of a sunspot — not just any sunspot, but one at a high solar latitude and with magnetic polarity opposite that of its predecessors. Scientists knew something like this was in the offing. A magnetic cluster seen in mid-December had the looked-for polarity and position in the Sun's northern hemisphere. It just hadn't coalesced into a distinct spot. Sunspots, caused by magnetic knots, look dark because they are a few thousand degrees cooler than the surrounding surface. When more sunspots pop up, so do solar flares and the more powerful coronal mass ejections (CMEs), the most violent explosions in our solar system. Both flares and CMEs can hurtle "storms" of superheated particles, X-rays and ultraviolet radiation toward Earth. Our planet's magnetic field generally does a good job of deflecting these storms, but satellites and astronauts can be vulnerable to harmful — even lethal — doses of radiation. Flares and CMEs can sizzle out power grids, interfere with communication and GPS satellites, and create dazzling auroras. In recent months the sunspot count has varied between zero and a few dozen, according to weekly reports sent to Sky & Telescope by a network of about 30 observers coordinated by Texas amateur Tom Fleming. But the numbers are certain to rise in the weeks and months ahead. Space-weather scientists are split on the strength and timing for Cycle 24's upcoming maximum. Some models predict a strong cycle (140 sunspots peaking in October 2011), while others portend a weak one (90 sunspots in August 2012). The "strong" proponents look at factors from preceding cycles, while the "weak" teams focus more on the poles' magnetic fields during the tapering of the previous cycle. Predicting sunspot cycles is an emerging field. This is only the third time scientists have attempted to forecast the Sun's activity, but they're gaining experience and confidence. The sooner more sunspots with traits like this one start springing up, the more likely the new cycle will be a strong one, with more frequent solar outbursts. If sunspots don't appear in droves by the middle of next year, it may be a weaker cycle.
Word from the orbit gurus at the Jet Propulsion Laboratory is that the impact watch for Mars is officially "off." On January 9th they announced that the odds of tiny 2007 WD 5 crashing into Mars on January 30th have dropped precipitously, to about 1 in 10,000 (0.01%). Instead, the two should come no closer than about 16,000 miles.
 The University of Hawaii's 2.2-meter (88-inch) telescope on Mauna Kea, Hawaii, captured asteroid 2007 WD5 (circled) on January 8–9, 2008. Other dots are artifacts from cosmic rays. The stars are trailed because the telescope tracked the asteroid as it moved among the stars. D. Tholen / F. Bernardi / M. Micheli This near miss was the likely outcome all along, but uncertainty remained until some big telescopic guns weighed in earlier this week with updated tracking observations. Estimated to be no more than 150 feet across, the asteroid is a dim 24th-magnitude blip and getting fainter as it moves outward from Earth and toward Mars.
Over the past few weeks astronomers have responded to this "will it or won't it?" situation just as they should have. A possible impactor was found, its projected track (though wildly uncertain) showed that a collision couldn't be ruled out, and the call went out for additional observations that eventually settled the matter.
Because the drama surrounding 2007 WD5 played out 50 million miles away, we were all spared the sensational news-media hype that usually surrounds these "killer asteroid" stories.
In discussions among the scientists involved, a few hold the opinion that the public becomes needlessly agitated when they learn that some space rock has a 1-in-XXXX chance of hitting Earth, only to learn later that additional observations have ruled it out. Others say that being able to watch the probability game play out is a good thing, a demonstration of how science actually "works."
What do you think?
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Posted: January 14, 2008The Ulysses spacecraft today is making a rare flyby of the sun's north pole. Unlike any other spacecraft, Ulysses is able to sample winds at the sun's poles, which are difficult to study from Earth. 
Artist concept of Ulysses making a north polar pass. Credit: NASA/JPL
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Ulysses has flown over the sun's poles three times before, in 1994-95, 2000-01 and 2007. Last week, solar physicists announced the first indications of a new solar cycle. Visiting the pole at this time may lead to new insights about solar activity. "This is a wonderful opportunity to examine the sun's north pole within a transition of cycles," said Arik Posner, Ulysses program scientist at NASA Headquarters in Washington. "We've never done this before." Many researchers believe the sun's poles are central to the 11-year ebb and flow of solar activity. When sunspots break up, their decaying magnetic fields are carried poleward by vast currents of plasma. This makes the poles a sort of graveyard for sunspots. Old magnetic fields sink beneath the polar surface 200,000 kilometers deep (about 124,000 miles), all the way down to the sun's inner magnetic dynamo, which generates the solar magnetic field. There, dynamo action amplifies the fields for use in future solar cycles. "Just as Earth's poles are crucial to studies of terrestrial climate change, the sun's poles may be crucial to studies of the solar cycle," said Ed Smith, Ulysses project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. Each previous flyby revealed something interesting and mysterious. One puzzle has been the temperature of the sun's poles. In the previous solar cycle, the magnetic north pole was about 80,000 degrees Fahrenheit (more than 44,000 degrees Celsius), or 8 percent cooler than the south. The current flyby may help solve this puzzle because it comes less than a year after a similar south pole flyby in Feb. 2007. Mission scientists will be able to compare temperature measurements, north versus south, with hardly any gap between them. Ulysses also discovered the sun's high-speed polar wind. At the sun's poles, the magnetic field opens up and allows solar atmosphere to stream out at a million miles per hour. By flying around the sun, covering all latitudes in a way that no other spacecraft can, Ulysses has been able to monitor this polar wind throughout the solar cycle and has found that it is acting a bit odd. "Twelve years ago, just before the previous 'sea change' between solar cycles, the polar wind spilled down almost all the way to the sun's equator. But this time it is not. The polar wind is bottled up, confined to latitudes above 45 degrees, " said Posner. Launched in Oct. 1990 from the space shuttle Discovery, Ulysses is a joint mission of NASA and the European Space Agency.
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