Author: Fraser Cain

Spiral galaxy NGC 3190. Image credit: ESO. Click to enlarge
Supernovae are rare enough, but astronomers discovered two going off in galaxy NGC 3190 at the same time. NGC 3190 is a large spiral galaxy that we see nearly edge on. Its shape has been warped through interactions between other nearby galaxies, and it has an active galactic nucleus. Astronomers uncovered one supernova in the southeastern part in March 2002, and then another team uncovered a second supernova on the other side two months later. This photograph of NGC 3190 was taken by ESO’s Very Large Telescope.

his beautiful edge-on spiral galaxy with tightly wound arms and a warped shape that makes it resemble a gigantic potato crisp lies in the constellation Leo (‘the Lion’) and is approximately 70 million light years away. It is the dominant member of a small group of galaxies known as Hickson 44, named after the Canadian astronomer, Paul Hickson. In addition to NGC 3190, Hickson 44 consists of one elliptical and two spiral galaxies. These are, however, slightly out of the field of view and therefore not visible here.

In 1982, Hickson published a catalogue of over 400 galaxies found in compact, physically-related groups of typically 4 to 5 galaxies per group (see the image of Robert’s Quartet in ESO PR Photo 34/05 as another example). Such compact groups allow astronomers to study how galaxies dynamically affect each other, and help them test current ideas on how galaxies form. One idea is that compact groups of galaxies, such as Hickson 44, merge to form a giant elliptical galaxy, such as NGC 1316 (see ESO PR 17/00).

Indeed, signs of tidal interactions are visible in the twisted dust lane of NGC 3190. This distortion initially misled astronomers into assigning a separate name for the southwestern side, NGC 3189, although NGC 3190 is the favoured designation.

NGC 3190 has an ‘Active Galactic Nucleus’, and as such, the bright, compact nucleus is thought to host a supermassive black hole.

In March 2002, a new supernova (SN 2002bo) was found in between the ‘V’ of the dust lanes in the southeastern part of NGC 3190. It was discovered independently by the Brazilian and Japanese amateur astronomers, Paulo Cacella and Yoji Hirose. SN 2002bo was caught almost two weeks before reaching its maximum brightness, allowing astronomers to study its evolution. It has been the subject of intense monitoring by a world-wide network of telescopes. The conclusion was that SN 2002bo is a rather unusual Type Ia supernova. The image presented here was taken in March 2003, i.e. about a year after the maximum of the supernova which is 50 times fainter on the image than a year before.

While observing SN 2002bo in May 2002, a group of Italian astronomers discovered another supernova, SN 2002cv, on the other side of NGC 3190. Two supernovae of this type appearing nearly simultaneously in the same galaxy is a rare event, as normally astronomers expect only one such event per century in a galaxy. SN 2002cv was best visible at infrared wavelengths as it was superimposed on the dust lane of NGC 3190, and therefore hidden by a large quantity of dust. In fact, this supernova holds the record for the most obscured Type Ia event.

The image was obtained with a total exposure time of 14 minutes only. Yet, with the amazing power of the Very Large Telescope, it reveals a large zoo of galaxies of varying morphologies. How many can you find?

Original Source: ESO News Release

NASA’s Swift captured this image of 73P/Schwassmann-Wachmann 3 as it bypassed the Ring Nebula. Image credit: NASA. Click to enlarge
Comet 73P/Schwassmann-Wachmann 3 is visible in the night sky with even a small backyard telescope, and it will make its closest approach to Earth next week (don’t worry, it’s still really far away). One of the features of this comet, however, is that it’s unusually bright in the X-ray spectrum. Three X-ray observatories will observe the comet in the coming weeks to determine what it’s made of, and maybe even the composition of the solar wind that causes its tail.

Scientists using NASA’s Swift satellite have detected X-rays from a comet that is now passing the Earth and rapidly disintegrating on what could be its final orbit around the sun.

Swift’s observations provide a rare opportunity to investigate several ongoing mysteries about comets and our solar system, and hundreds of scientists have tuned in to the event.

The comet, called 73P/Schwassmann-Wachmann 3, is visible with even a small, backyard telescope. Peak brightness is expected next week, when it comes within 7.3 million miles of Earth, or about 30 times the distance to the Moon. There is no threat to Earth, however.

This is the brightest comet ever detected in X-rays. The comet is so close that astronomers are hoping to determine not only the composition of the comet but also of the solar wind. Scientists think that atomic particles that comprise the solar wind interact with comet material to produce X-rays, a theory that Swift might prove true.

Three world-class X-ray observatories now in orbit—NASA’s Chandra X-ray Observatory, the European-led XMM-Newton, and the Japanese-led Suzaku—will observe the comet in the coming weeks. Like a scout, Swift has provided information to these larger facilities about what to look for. This type of observation can only take place in the X-ray waveband.

“The Schwassmann-Wachmann comet is a comet like no other,” said Scott Porter of NASA’s Goddard Space Flight Center in Greenbelt, Md., part of the Swift observation team. “During its 1996 passage it broke apart. Now we are tracking about three dozen fragments. The X-rays being produced provide information never before revealed.”

The situation is reminiscent of the Deep Impact probe, which penetrated comet Tempel 1 about a year ago. This time, nature itself has broken the comet. Because Schwassmann-Wachmann 3 is much closer to both the Earth and the sun than Tempel 1 was, it currently appears about 20 times brighter in X-rays. Schwassmann-Wachmann 3 passes Earth about every five years. Scientists could not anticipate how bright it would become in X-rays this time around.

“The Swift observations are amazing,” said Greg Brown of Lawrence Livermore National Laboratory in Livermore, Calif., who led the proposal for Swift observation time. “Because we are viewing the comet in X-rays, we can see many unique features. The combined results of data from several premier orbiting observatories will be spectacular.”

Swift is primarily a gamma-ray burst detector. The satellite also has X-ray and ultraviolet/optical telescopes. Because of its burst-hunting ability to turn rapidly, Swift has been able to track the progress of the fast-moving Schwassmann-Wachmann 3 comet. Swift is the first observatory to simultaneously observe the comet in both ultraviolet light and X-rays. This cross comparison is crucial for testing theories about comets.

Swift and the other three X-ray observatories plan to combine forces to observe Schwassmann-Wachmann 3 closely. Through a technique called spectroscopy, scientists hope to determine the chemical structure of the comet. Already Swift has detected oxygen and hints of carbon. These elements are from the solar wind, not the comet.

Scientists think that X-rays are produced through a process called charge exchange, in which highly (and positively) charged particles from the sun that lack electrons steal electrons from chemicals in the comet. Typical comet material includes water, methane and carbon dioxide. Charge exchange is analogous to the tiny spark seen in static electricity, only at a far greater energy.

By comparing the ratio of X-ray energies emitted, scientists can determine the content of the solar wind and infer the content of the comet material. Swift, Chandra, XMM-Newton and Suzaku each provide complementary capabilities to nail down this tricky measurement. The combination of these observations will provide a time evolution of the X-ray emission of the comet as it navigates through our solar system.

Porter and his colleagues at Goddard and Lawrence Livermore tested the charge exchange theory in an earthbound laboratory in 2003. That experiment, at Livermore’s EBIT-I electron beam ion trap, produced a complex spectrograph of intensity versus X-ray energy for a variety of expected elements in the solar wind and comet. “We are anxious to compare nature’s laboratory to the one we created,” Porter said.

The German-led ROSAT mission, now decommissioned, was the first to detect X-rays from a comet, from Hyakutake in 1996. This was a great surprise. It took about five years before scientists had a suitable explanation for X-ray emission. Now, ten years after Hyakutake, scientists could settle the mystery.

Original Source: NASA News Release

A schematic view of the new SDSS three-dimensional map. Image credit: Hogg/SDSS-II collaboration. Click to enlarge
Astronomers from UC Berkeley have created the most comprehensive three-dimensional map of the Universe ever published. Amazingly, this map is merely a slice containing 1/10th of the northern hemisphere. It contains 600,000 galaxies and extends out 5.6 billion light-years into space. This map allows astronomers to study evidence for dark energy – the mysterious force accelerating the expansion of the Universe.

A team of astronomers led by Nikhil Padmanabhan and David Schlegel has published the largest three-dimensional map of the universe ever constructed, a wedge-shaped slice of the cosmos that spans a tenth of the northern sky, encompasses 600,000 uniquely luminous red galaxies, and extends 5.6 billion light-years deep into space, equivalent to 40 percent of the way back in time to the Big Bang.

Schlegel is a Divisional Fellow in the Physics Division of Lawrence Berkeley National Laboratory, and Padmanabhan will join the Lab’s Physics Division as a Chamberlain Fellow and Hubble Fellow in September; presently he is at Princeton University. They and their coauthors are members of the Sloan Digital Sky Survey (SDSS), and have previously produced smaller 3-D maps by using the SDSS telescope in New Mexico to painstakingly collect the spectra of individual galaxies and calculate their distances by measuring their redshifts.

“What’s new about this map is that it’s the largest ever,” says Padmanabhan, “and it doesn’t depend on individual spectra.”

The principal motive for creating large-scale 3-D maps is to understand how matter is distributed in the universe, says Padmanabhan. “The brightest galaxies are like lighthouses – where the light is, is where the matter is.”

Schlegel says that “because this map covers much larger distances than previous maps, it allows us to measure structures as big as a billion light-years across.”

The variations in galactic distribution that constitute visible large-scale structures are directly descended from variations in the temperature of the cosmic microwave background, reflecting oscillations in the dense early universe that have been measured to great accuracy by balloon-borne experiments and the WMAP satellite.

The result is a natural “ruler” formed by the regular variations (sometimes called “baryon oscillations,” with baryons as shorthand for ordinary matter), which repeat at intervals of some 450 million light-years.

“Unfortunately it’s an inconveniently sized ruler,” says Schlegel. “We had to sample a huge volume of the universe just to fit the ruler inside.”

Says Padmanabhan, “Although the universe is 13.7 billion years old, that really isn’t a whole lot of time when you’re measuring with a ruler that’s marked only every 450 million light-years.”

The distribution of galaxies reveals many things, but one of the most important is a measure of the mysterious dark energy that accounts for some three-fourths of the universe’s density. (Dark matter accounts for roughly another 20 percent, while less than 5 percent is ordinary matter of the kind that makes visible galaxies.)

“Dark energy is just the term we use for our observation that the expansion of the universe is accelerating,” Padmanabhan remarks. “By looking at where density variations were at the time of the cosmic microwave background” – only about 300,000 years after the Big Bang – “and seeing how they evolve into a map that covers the last 5.6 billion years, we can see if our estimates of dark energy are correct.”

The new map shows that the large-scale structures are indeed distributed the way current ideas about the accelerating expansion of the universe would suggest. The map’s assumed distribution of dark matter, which although invisible is affected by gravity just like ordinary matter, also conforms to current understanding.

What made the big new 3-D map possible were the Sloan Digital Sky Survey’s wide-field telescope, which covers a three-degree field of view (the full moon is about half a degree), plus the choice of a particular kind of galactic “lighthouse,” or distance marker: luminous red galaxies.

“These are dead, red galaxies, some of the oldest in the universe – in which all the fast-burning stars have long ago burned out and only old red stars are left,” says Schlegel. “Not only are these the reddest galaxies, they’re also the brightest, visible at great distances.”

The Sloan Digital Sky Survey astronomers worked with colleagues on the Australian Two-Degree Field team to average the color and redshift of a sample of 10,000 red luminous galaxies, relating galaxy color to distance. They then applied these measurements to 600,000 such galaxies to plot their map.

Padmanabhan concedes that “there’s statistical uncertainty in applying a brightness-distance relation derived from 10,000 red luminous galaxies to all 600,000 without measuring them individually. The game we play is, we have so many that the averages still give us very useful information about their distribution. And without having to measure their spectra, we can look much deeper into space.”

Schlegel agrees that the researchers are far from achieving the precision they want. “But we have shown that such measurements are possible, and we have established the starting point for a standard ruler of the evolving universe.”

He says “the next step is to design a precision experiment, perhaps based on modifications to the SDSS telescope. We are working with engineers here at Berkeley Lab to redesign the telescope to do what we want to do.”

“The Clustering of Luminous Red Galaxies in the Sloan Digital Sky Survey Imaging Data,” by Nikhil Padmanabhan, David J. Schlegel, Uros Seljak, Alexey Makarov, Neta A. Bahcall, Michael R. Blanton, Jonathan Brinkmann, Daniel J. Eisenstein, Douglas P. Finkbeiner, James E. Gunn, David W. Hogg, ??bf?eljko Ivezić, Gillian R. Knapp, Jon Loveday, Robert H. Lupton, Robert C. Nichol, Donald P. Schneider, Michael A. Strauss, Max Tegmark, and Donald G. York, will appear in the Monthly Notices of the Royal Astronomical Society and is now available online at http://arxiv.org/archive/astro-ph.

SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions, which are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, Cambridge University, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.

SDSS funding is provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. Visit the SDSS web site at http://www.sdss.org/.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our website at http://www.lbl.gov.

Original Source: Berkeley Lab