Many galaxies have super-massive black holes at their core, which expel powerful jets of particles at nearly the speed of light. Using the National Radio Astronomy Observatory's very long baseline array, scientists recently confirmed the leading theory, according to which the particles are accelerated by tightly-twisted magnetic fields close to the black hole.
Just how the powerful particle jets are emitted from black holes was one of the big mysteries of astrophysics. The confirmation of the leading theory, according to which the particles are accelerated by magnetic fields, required an elusive close-up view of the particle jet's inner throat. Astronomers managed to observe the material winding in a corkscrew outward path thanks to the high resolution of the National Radio Astronomy Observatory's very long baseline array (VLBA), an observation that supports the magnetic field theory.
The international team studied a galaxy named BL Lacertae (BL Lac), situated some 950 million light-years away from Earth. BL Lac is a blazar, the most energetic type of black-hole-powered galactic core. Super-massive black holes in galaxies' cores power jets of particles and intense radiation in similar objects, including quasars and seyfert galaxies. The scientists chose to focus on the BL Lacertae Galaxy because of the high rate in which the phenomena occur in that region.
According to the theory, the phenomena occur in stages. When material is pulled inward towards the black hole, it forms a flattened, rotating disk, called an accretion disk. As the material moves from the outer edge of the disk inward, magnetic field lines perpendicular to the disk are twisted, forming a tightly-coiled bundle. Astronomers believe that this 'bundle' propels and confines the ejected particles. Closer to the black hole, space itself, including the magnetic fields, is twisted by the strong gravitational pull and rotation of the black hole, causing the emission of the particles.
Theorists have several predictions concerning material and light in these situations. The first speculation is that material moving outward in this close-in acceleration region will follow a corkscrew-shaped path inside the bundle of twisted magnetic fields. The second prediction is that light and other radiation emitted by the moving material will brighten when its rotating path is aimed most directly towards Earth.
When the team observed an outburst from BL Lac, Alan Marscher of Boston University, who led the team, said that: "That behavior is exactly what we saw." During the numerous observations, the astronomers noticed that as the material sped out from the neighborhood of the black hole, the VLBA could pinpoint its location. Other telescopes measured the properties of the radiation emitted from the knot. It appears that the theories are very precise: bright bursts of light, X-rays, and gamma rays occurred when the knot was at the exact locations predicted by the theories. In addition, the alignment of the radio and light waves (a property called polarization) rotated as the knot wound its corkscrew path inside the tight throat of twisted magnetic fields. According to Marscher, this observation gave the researchers an unprecedented view of the inner portion of one of these jets, and therefore, they gained information critical to the understanding of how these particle accelerators work.
Obviously, the researchers were excited about the new discovery. "We have gotten the clearest look yet at the innermost portion of the jet, where the particles actually are accelerated, and everything we see supports the idea that twisted, coiled magnetic fields are propelling the material outward," Marscher said. It is evident that this is a major advance in the understanding of a remarkable process which occurs throughout the Universe.
TFOT has reported on images of the Triangulum Galaxy, which were captured during over 11 hours of exposure time, and on the discovery of the building blocks of life in space, made using NASA's Spitzer Space Telescope. Other related TFOT stories are the detection of the largest known comet outburst and a new explanation of the way the Peruvian Meteorite made it to Earth, given by an expert in extraterrestrial impacts from Brown University.
These images taken by NASA's Hubble Space Telescope show nine compact, ultradense galaxies as they appeared 11 billion years ago.
By SPACE.com Staff
Several newfound galaxies seen as they existed when the universe was young are packed with improbable numbers of stars.
Astronomers don't know what's going on.
The nine galaxies are 11 billion light-years away, which means the light astronomers are looking at left the galaxies 11 billion years ago, when the universe was less than 3 billion years old.
Each of the newly studied galaxies weighs about 200 billion times the mass of the sun yet is a mere 5,000 light-years across. Our Milky Way Galaxy is a fraction of that heft at roughly 3 million times the sun's mass, and yet it stretches across 100,000 light-years of space.
The compact galaxies have been furiously forming stars; each contains as many stars as a typical large galaxy of today, the new observations reveal.
"Seeing the compact sizes of these galaxies is a puzzle," said Pieter G. van Dokkum of Yale University, who led the study. "No massive galaxy at this distance has ever been observed to be so compact."
Since no modern galaxies — galaxies in the nearby universe — are so compact, the scientists assume compact galaxies from the early universe must have gotten much larger as they matured beyond the snapshots of ancient time now being studied. But nobody knows how.
"They would have to change a lot over 11 billion years, growing five times bigger," van Dokkum said. "They could get larger by colliding with other galaxies, but such collisions may not be the complete answer."
Astronomers used NASA's Hubble Space Telescope and the W.M. Keck Observatory on Mauna Kea, Hawaii to make the new observations, which were announced today and were detailed in the April 10 issue of the Astrophysical Journal Letters.
Van Dokkum and his colleagues had previously studied the galaxies in 2006 with the Gemini South Telescope to determine their distances, and showed that the stars are a half a billion to a billion years old. The most massive stars had already exploded as supernovae.
One reason these galaxies were so dense, van Dokkum suggested, involves the interaction of dark matter and hydrogen gas in the nascent universe. Dark matter is an invisible form of matter that accounts for most of the universe's mass. Shortly after the theoretical Big Bang, the universe contained an uneven landscape of dark matter. Hydrogen gas became trapped in puddles of the invisible material, the thinking goes, and began spinning rapidly in dark matter's gravitational whirlpool, forming stars at a furious rate.
Based on the galaxies' mass, the astronomers estimated that the stars are spinning around their galactic disks at roughly 890,000 to 1 million mph (400 to 500 kilometers a second). Stars in today's galaxies, by contrast, are traveling at about half that speed because the setups are larger and rotate more slowly.
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WASHINGTON (Reuters) - Images of colliding galaxies show them spinning, sliding and slipping into one another, wreaking stellar destruction that will give birth to new and larger galaxies.
The Maryland-based Space Telescope Science Institute released 59 new images from the Hubble Space Telescope on Thursday to celebrate the 18th anniversary of its launch.
"This new Hubble atlas dramatically illustrates how galaxy collisions produce a remarkable variety of intricate structures in never-before-seen detail," the Institute said in a statement.
"Astronomers observe only one out of a million galaxies in the nearby universe in the act of colliding. However, galaxy mergers were much more common long ago when they were closer together, because the expanding universe was smaller."
The color images, available online, are a look back in time. It takes hundreds of millions of years for galaxies to merge and the light from their stars has traveled for hundreds of millions of years across space.
Because it orbits outside the Earth's atmosphere, Hubble's cameras can take extremely sharp images.
Its future was controversial, as it requires regular servicing by space shuttle astronauts to stay in working condition.
After the 2003 Columbia space shuttle disaster, a servicing mission initially planned for 2004 was canceled.
NASA at one point was planning to abandon the telescope, hugely popular among astronomers. After an outcry, the U.S. space agency relented and a final Hubble servicing mission is scheduled for August.
In 2013, the James Webb Space Telescope is scheduled to replace Hubble
ABC News has been given unprecedented access to the astronauts, scientists and engineers involved in the intensive — and some say risky — shuttle mission to repair the Hubble Space Telescope later this year.
Time is running out for Hubble. If its batteries and gyroscopes aren't replaced soon, the most famous of space telescopes will simply quit functioning.
If all goes well, the Space Shuttle Atlantis mission, dubbed STS 125, will launch in August to service Hubble. ABC News will follow the crew as it trains for this mission.
This will be the last time a space shuttle visits Hubble. Everyone involved knows they must make every single minute of the mission count to ensure Hubble will continue to explore the universe until the replacement Webb telescope can be launched sometime in the next decade.
What makes this mission risky?
Unlike most recent shuttle missions, this one will not be docking at the International Space Station. If Atlantis encounters an emergency, Hubble's orbit is so far from the space station, that the Atlantis crew will not be able to reach it.
But NASA is ready with an unprecedented backup plan. For the first time, when the Atlantis astronauts launch to repair Hubble, a second shuttle will already be on the other launch pad at the Kennedy Space Center, ready to go within days if its colleagues on the Hubble mission encounter a problem.
It is easy to see why the Hubble mission is the most talked about mission of the year at NASA and overshadows the global effort to build the International Space Station.
Hubble is the telescope that can look back in time; the space station is still a construction project, albeit one of the most complicated ever undertaken.
Just what kind of allure does the Hubble Space Telescope have that the International Space Station doesn't? Apollo 7 astronaut Walt Cunningham says it's all about perception.
"The International Space Station is the most incredible engineering achievement in history. It exceeds the Panama Canal or the pyramids if you will, but it doesn't capture the public's fancy, because it looks like a truck driving back and forth delivering construction materials," he said.
Hubble was deployed in 1990, and it wasn't an instant hit. Its first images were blurry because of an embarrassing failure to notice that the shape of the telescope's primary mirror was not accurate.
A daring space shuttle mission to install corrective lenses fixed that in 1993. That troubled beginning is part of its mystique, according to Sandra Faber of the University of California at Santa Cruz.
"It was such a disaster, but it was like chestnuts pulled out of the fire at the last minute. It is the ultimate American can-do story," she said.
And oh what Hubble can do! Hubble has allowed scientists to estimate the age of the universe — 14 billion years.
Faber points to Hubble's discoveries about galaxies. "First and foremost for me as [a] student of galaxy formation, Hubble was the first telescope to look back in time and show us infant galaxies, in the process of being born. That's a first. To use a telescope as a time machine looking back billions of years — that is a terrific legacy."
Matt Mountain, director of the Hubble Space Telescope, says the telescope's popularity is simple to explain.
"It allows us to see the universe in a way we don't have to explain. A picture is worth 1,000 words and so we look back in time at some of the earliest galaxies," he said.
"What we deliver back are stunning images of these fairly early galaxies," Mountain said. "And so we can't disassociate science from the image because there's actually great meaning in the science and the public actually engages in that when they look at these great pictures."
Steve Hawley is one of the astronauts who deployed Hubble. He is also an astronomer and thinks he understands why Hubble resonates with so many people.
"The pictures are breathtaking; the science discoveries are mind boggling. I will be sitting next to someone on an airplane and they will ask me what do I do, and I say I work for NASA and they'll say 'oh NASA,' and they think the shuttle goes to the moon and we launch from Houston but they know about Hubble."
What makes people remember Hubble when they aren't ordinarily interested in space? Hawley has wondered about that.
"Whatever it turns out to be we need to learn that lesson because we need to apply it to other things we are doing. If it's the pictures, if it's the drama is, you know you can always pick up the paper and read something new Hubble has done, maybe people think they are getting value for their tax dollars, but as far as I know we never really studied it, or asked someone who knows how to do that kind of thing to study it, and tell us what it really was about Hubble that people found so appealing."
By Jeremy Hsu
16 April 2008
A telescope on the far side of the moon could probe the "dark ages" of the universe while blocking out the radio-wavelength noise of Earth civilizations.
Up to one hundred thousand antennas would form the Dark Ages Lunar Interferometer (DALI), the largest telescope ever built, and allow astronomers to hear faint whispering signals from a time when no stars even existed.
"This will look at one of the most fundamental questions ever conceived, back when the universe was made up almost entirely of hydrogen and helium — no stars, no galaxies," said Kurt Weiler, senior astronomer at the U.S. Naval Research Laboratory.
The so-called dark ages of astronomy describe a half-billion year period following the Big Bang when clouds of ionized gas cooled as the universe expanded. The only faint noise came from hydrogen atoms doing spin-flips, which gives off radio-wavelength signals that astronomers can pick up on. Scientists currently estimate that the universe is about 13.7 billion years old.
"What happens is that because of the Big Bang there's a background glow," Weiler noted. "The spin-flip will absorb the glow of the older material and will give us a signature that we can see."
However, the ongoing expansion of the universe has stretched or red-shifted the hydrogen signature from just 21 centimeters to several meters. That means the signals can easily get masked by louder Earth transmissions in the same wavelength, unless astronomers find a quieter listening spot.
"The back side of the moon is the only place in the local universe shielded from manmade transmissions," Weiler told SPACE.com.
The DALI design resembles existing radio telescope arrays in the Netherlands, Australia, and New Mexico. But sending such an array to the moon requires lighter material that can save on launch costs, not to mention survive the harsh lunar conditions.
One candidate is polyimide, a plastic-like film which can act as an antenna when plated with metal. University of Colorado researchers are testing the film's durability by exposing it to harsh ultraviolet rays, as well as the extreme temperatures like that of boiling water and super-cold liquid nitrogen.
The film antennas would be rolled up and then unrolled for deployment across 30 miles (48 km) of lunar surface, arrayed in one thousand stations containing one hundred antennas each. Still, getting the entire load to the moon represents a challenge.
"Even though each antenna may weigh a few ounces, you're talking about needing at least heavy lift vehicles," Weiler noted. "They all add up fast."
The U.S. Naval Research Laboratory is sharing NASA funding with an MIT-based team working on another lunar telescope separate from DALI. Their collaboration may finally realize a dream that many astronomers had even before the first Apollo landings on the moon.
"Probing the dark ages presents the opportunity to watch the young Universe evolve," said Joseph Lazio, NRL astronomer and head of the DALI proposal. "Just as current cosmological studies have both fascinated and surprised us, I anticipate that DALI will lead both to increased understanding of the Universe and unexpected discoveries."
