Note: Gamma Ray Bursts are covered in Chapter 32
Shapley-Curtis Debate
Anglo-Australian Observatory
European
Southern Observatory
Hubble Space Telescope
Chandra X-Ray Observatory
Very Large Array
Australia Telescope
Simulations of
Colliding Galaxies
Debate
on the Scale of the Universe
The Messier Page
A Searchable Set of Astronomical
Images
Galaxy Course Notes from William
Keel
Galaxy Images from William Keel
Farhad Yusef-Zadeh's combination images; optical vs. radio
NASA Extragalactic Database
Simbad Database
Spitzer View of Galaxy M81
Spitzer Spectrum of Organic Materials in a Galaxy
Astronomers at the Space Telescope Science Institute today unveiled the deepest portrait of the visible universe ever achieved by humankind. Called the Hubble Ultra Deep Field (HUDF), the million-second-long exposure reveals the first galaxies to emerge from the so-called "dark ages," the time shortly after the big bang when the first stars reheated the cold, dark universe. The new image should offer new insights into what types of objects reheated the universe long ago.
This historic new view is actually two separate images taken by Hubble's Advanced Camera for Surveys (ACS) and the Near Infrared Camera and Multi-object Spectrometer (NICMOS). Both images reveal galaxies that are too faint to be seen by ground-based telescopes, or even in Hubble's previous faraway looks, called the Hubble Deep Fields (HDFs), taken in 1995 and 1998.
"Hubble takes us to within a stone's throw of the big bang itself," says Massimo Stiavelli of the Space Telescope Science Institute in Baltimore, Md., and the HUDF project lead. The combination of ACS and NICMOS images will be used to search for galaxies that existed between 400 and 800 million years (corresponding to a redshift range of 7 to 12) after the big bang. A key question for HUDF astronomers is whether the universe appears to be the same at this very early time as it did when the cosmos was between 1 and 2 billion years old.
The HUDF field contains an estimated 10,000 galaxies. In ground-based images, the patch of sky in which the galaxies reside (just one-tenth the diameter of the full Moon) is largely empty. Located in the constellation Fornax, the region is below the constellation Orion.
The final ACS image, assembled by Anton Koekemoer of the Space Telescope Science Institute, is studded with a wide range of galaxies of various sizes, shapes, and colors. In vibrant contrast to the image's rich harvest of classic spiral and elliptical galaxies, there is a zoo of oddball galaxies littering the field. Some look like toothpicks; others like links on a bracelet. A few appear to be interacting. Their strange shapes are a far cry from the majestic spiral and elliptical galaxies we see today. These oddball galaxies chronicle a period when the universe was more chaotic. Order and structure were just beginning to emerge.
Installed in 2002 during the last servicing mission to the Hubble telescope, the ACS has twice the field of view and a higher sensitivity than the older workhorse camera, the Wide Field Planetary Camera 2, installed during the 1993 servicing mission. "The large discovery efficiency of the ACS is now being exploited in sky surveys such as the HUDF," Stiavelli says.
The NICMOS sees even farther than the ACS. The NICMOS reveals the farthest galaxies ever seen, because the expanding universe has stretched their light into the near-infrared portion of the spectrum. "The NICMOS provides important additional scientific content to cosmological studies in the HUDF," says Rodger Thompson of the University of Arizona and the NICMOS Principal Investigator. The ACS uncovered galaxies that existed 800 million years after the big bang (at a redshift of 7). But the NICMOS may have spotted galaxies that lived just 400 million years after the birth of the cosmos (at a redshift of 12). Thompson must confirm the NICMOS discovery with follow-up research.
"The images will also help us prepare for the next step from NICMOS on the Hubble telescope to the James Webb Space Telescope (JWST)," Thompson explains. "The NICMOS images reach back to the distance and time that JWST is destined to explore at much greater sensitivity." In addition to distant galaxies, the longer infrared wavelengths are sensitive to galaxies that are intrinsically red, such as elliptical galaxies and galaxies that have red colors due to a high degree of dust absorption.
The entire HUDF also was observed with the advanced camera's "grism" spectrograph, a hybrid prism and diffraction grating. "The grism spectra have already yielded the identification of about a thousand objects. Included among them are some of the intensely faint and red points of light in the ACS image, prime candidates for distant galaxies," says Sangeeta Malhotra of the Space Telescope Science Institute and the Principal Investigator for the Ultra Deep Field's ACS grism follow-up study. "Based on those identifications, some of these objects are among the farthest and youngest galaxies ever seen. The grism spectra also distinguish among other types of very red objects, such as old and dusty red galaxies, quasars, and cool dwarf stars."
Galaxies evolved so quickly in the universe that their most important changes happened within a billion years of the big bang. "Where the HDFs showed galaxies when they were youngsters, the HUDF reveals them as toddlers, enmeshed in a period of rapid developmental changes," Stiavelli says.
Hubble's ACS allows astronomers to see galaxies two to four times fainter than Hubble could view previously, and is also very sensitive to the near-infrared radiation that allows astronomers to pluck out some of the farthest observable galaxies in the universe. This will hold the record as the deepest-ever view of the universe until ESA, together with NASA, launches the James Webb Space Telescope in 2011.
Though ground-based telescopes have, to date, spied objects that existed just 500 million years after the big bang (at a redshift of 10), they need the help of a rare natural zoom lens in space, called a gravitational lens, to see them. However, the ACS can reveal typical galaxies at these great distances. Even much larger ground-based telescopes with adaptive optics cannot reproduce such a view. The ACS picture required a series of exposures taken over the course of 400 Hubble orbits around Earth. This is such a big chunk of the telescope's annual observing time that Institute Director Steven Beckwith used his own Director's Discretionary Time to provide the needed resources.
The HUDF observations began Sept. 24, 2003 and continued through Jan. 16, 2004. The telescope's ACS camera, the size of a phone booth, captured ancient photons of light that began traversing the universe even before Earth existed. Photons of light from the very faintest objects arrived at a trickle of one photon per minute, compared with millions of photons per minute from nearer galaxies.
Just like the previous HDFs, the new data are expected to galvanize the astronomical community and lead to dozens of research papers that will offer new insights into the birth and evolution of galaxies.
Electronic images and additional information are available at:A collision of two galaxies has left a merged star system with an unusual appearance as well as bizarre internal motions. Messier 64 (M64) has a spectacular dark band of absorbing dust in front of the galaxy's bright nucleus, giving rise to its nicknames of the "Black Eye" or "Evil Eye" galaxy.
This image of M64 was taken with Hubble's Wide Field Planetary Camera 2 (WFPC2) in 2001. The color image is a composite prepared by the Hubble Heritage Team from pictures taken through four different color filters. These filters isolate blue and near-infrared light, along with red light emitted by hydrogen atoms and green light from Strömgren y.
Image Credit: NASA and The Hubble Heritage Team (AURA/STScI) Acknowledgment: S. Smartt (Institute of Astronomy) and D. Richstone (U. Michigan)
To see and read more, please visit:An international team of astronomers may have set a new record in discovering what is the most distant known galaxy in the universe. Located an estimated 13 billion light-years away, the object is being viewed at a time only 750 million years after the big bang, when the universe was barely 5 percent of its current age.
The primeval galaxy was identified by combining the power of NASA's Hubble Space Telescope and CARA's W. M. Keck Telescopes on Mauna Kea in Hawaii. These great observatories got a boost from the added magnification of a natural "cosmic gravitational lens" in space that further amplifies the brightness of the distant object.
The Caltech team reporting on the discovery consists of Drs. Jean-Paul Kneib, Richard S. Ellis, Michael R. Santos and Johan Richard. Drs. Kneib and Richard also serve the Observatoire Midi-Pyrenees of Toulouse, France. Dr. Santos also represents the Institute of Astronomy, Cambridge, UK.
To see and read more, please visit:Using the ISAAC near-infrared instrument on ESO's Very Large Telescope, and the magnification effect of a gravitational lens, a team of French and Swiss astronomers [2] has found several faint galaxies believed to be the most remote known.
Further spectroscopic studies of one of these candidates has provided a strong case for what is now the new record holder - and by far - of the most distant galaxy known in the Universe.
Named Abell 1835 IR1916, the newly discovered galaxy has a redshift of 10 [3] and is located about 13,230 million light-years away. It is therefore seen at a time when the Universe was merely 470 million years young, that is, barely 3 percent of its current age.
This primeval galaxy appears to be ten thousand times less massive than our Galaxy, the Milky Way. It might well be among the first class of objects which put an end to the Dark Ages of the Universe.
This remarkable discovery illustrates the potential of large ground-based telescopes in the near-infrared domain for the exploration of the very early Universe.
The full text of this Press Release and the two associated ESO PR Photos 05a-b/04 are available.More precisely, astronomers are trying to explore the last "unknown territories", the boundary between the "Dark Ages" and the "Cosmic Renaissance".
Rather shortly after the Big Bang, which is now believed to have taken place some 13,700 million years ago, the Universe plunged into darkness. The relic radiation from the primordial fireball had been stretched by the cosmic expansion towards longer wavelengths and neither stars nor quasars had yet been formed which could illuminate the vast space. The Universe was a cold and opaque place. This sombre era is therefore quite reasonably dubbed the "Dark Ages".
A few hundred million years later, the first generation of stars and, later still, the first galaxies and quasars, produced intense ultraviolet radiation, gradually lifting the fog over the Universe.
This was the end of the Dark Ages and, with a term again taken over from human history, is sometimes referred to as the "Cosmic Renaissance".
Astronomers are trying to pin down when - and how - exactly the Dark Ages finished. This requires looking for the remotest objects, a challenge that only the largest telescopes, combined with a very careful observing strategy, can take up.
Further in the past, however, observations of galaxies and quasars become scarce. Currently, only a handful of very faint galaxies are seen approximately 1,200 to 750 million years after the Big Bang (redshift 5-7). Beyond that, the faintness of these sources and the fact their light is shifted from the optical to the near infrared has so far severely limited the studies.
An important breakthrough in this quest for the earliest formed galaxy has now been achieved by a team of French and Swiss astronomers [2] using ESO's Very Large Telescope (VLT) equipped with the near-infrared sensitive instrument ISAAC. To accomplish this, they had to combine the light amplification effect of a cluster of galaxies - a Gravitational Telescope - with the light gathering power of the VLT and the excellent sky conditions prevailing at Paranal.
First of all, very deep images of a cluster of galaxies named Abell 1835 were taken using the ISAAC near-infrared instrument on the VLT. Such relatively nearby massive clusters are able to bend and amplify the light of background sources - a phenomenon called Gravitational Lensing and predicted by Einstein's theory of General Relativity.
This natural amplification allows the astronomers to peer at galaxies which would otherwise be too faint to be seen. In the case of the newly discovered galaxy, the light is amplified approximately 25 to 100 times! Combined with the power of the VLT it has thereby been possible to image and even to take a spectrum of this galaxy. Indeed, the natural amplification effectively increases the aperture of the VLT from 8.2-m to 40-80 m.
The deep near-IR images taken at different wavelengths have allowed the astronomers to characterise the properties of a few thousand galaxies in the image and to select a handful of them as potentially very distant galaxies. Using previously obtained images taken at the Canada-France- Hawaii Telescope (CFHT) on Mauna Kea and images from the Hubble Space Telescope, it has then been verified that these galaxies are indeed not seen in the optical. In this way, six candidate high redshift galaxies were recognised whose light may have been emitted when the Universe was less than 700 million years old.
To confirm and obtain a more precise determination of the distance of one of these galaxies, the astronomers used again ISAAC on the VLT, but this time in its spectroscopic mode. After several months of careful analysis of the data, the astronomers are convinced to have detected a weak but clear spectral feature in the near-infrared domain. The astronomers have made a strong case that this feature is most certainly the Lyman-alpha emission line typical of these objects. This line, which occurs in the laboratory at a wavelength of 0.1216 micron, that is, in the ultraviolet, has been stretched to the near infrared at 1.34 micron, making Abell 1835 IR1916 the first galaxy known to have a redshift as large as 10.
From the images of this galaxy obtained in the various wavebands, the astronomers deduce that it is undergoing a period of intense star formation. But the amount of stars formed is estimated to be "only" 10 million times the mass of the sun, approximately ten thousand times smaller than the mass of our Galaxy, the Milky Way.
In other words, what the astronomers see is the first building block of the present-day large galaxies. This finding agrees well with our current understanding of the process of galaxy formation corresponding to a successive build-up of the large galaxies seen today through numerous mergers of "building blocks", smaller and younger galaxies formed in the past.
It is these building blocks which may have provided the first light sources that lifted the fog over the Universe and put an end to the Dark Ages.
For Roser Pello, from the Observatoire Midi-Pyrenees (France) and co-leader of the team, "these observations show that under excellent sky conditions like those at ESO's Paranal Observatory, and using strong gravitational lensing, direct observations of distant galaxies close to the Dark Ages are feasible with the best ground-based telescopes."
The other co-leader of the team, Daniel Schaerer from the Geneva Observatory and University (Switzerland), is excited: "This discovery opens the way to future explorations of the first stars and galaxies in the early Universe."
Additional explanations and images are available on the authors' web page.
Notes [1] This press release is issued in coordination between ESO, the Swiss National Science Foundation, the French Centre National de la Recherche Scientifique, and the European Journal Astronomy and Astrophysics."From the outset of the project in the late 80's, one of our key goals has been a precision measurement of how galaxies cluster under the influence of gravity", explained Richard Kron, SDSS's director and a professor at The University of Chicago.
SDSS Project spokesperson Michael Strauss from Princeton University and one of the lead authors on the new study elaborated that: "This clustering pattern encodes information about both invisible matter pulling on the galaxies and about the seed fluctuations that emerged from the Big Bang."Images of these seed fluctuations were released from the Wilkinson Microwave Anisotropy Probe (WMAP) in February, which measured the fluctuations in the relic radiation from the early Universe.
"We have made the best three-dimensional map of the Universe to date, mapping over 200,000 galaxies up to two billion light years away over six percent of the sky", said another lead author of the study, Michael Blanton from New York University. The gravitational clustering patterns in this map reveal the makeup of the Universe from its gravitational effects and, by combining their measurements with that from WMAP, the SDSS team measured the cosmic matter to consist of 70 percent dark energy, 25 percent dark matter and five percent ordinary matter.
They found that neutrinos couldn't be a major constituent of the dark matter, putting the strongest constraints to date on their mass. Finally, the SDSS research found that the data are consistent with the detailed predictions of the inflation model.
"Different galaxies, different instruments, different people and different analysis - but the results agree", says Max Tegmark from the University of Pennsylvania, first author on the two papers. "Extraordinary claims require extraordinary evidence", Tegmark says, "but we now have extraordinary evidence for dark matter and dark energy and have to take them seriously no matter how disturbing they seem."
"The real challenge is now to figure what these mysterious substances actually are", said another author, David Weinberg from Ohio State University."The SDSS is really two surveys in one", explained Project Scientist James Gunn of Princeton University. On the most pristine nights, the SDSS uses a wide-field CCD camera (built by Gunn and his team at Princeton University and Maki Sekiguchi of the Japan Participation Group) to take pictures of the night sky in five broad wavebands with the goal of determining the position and absolute brightness of more than 100 million celestial objects in one-quarter of the entire sky. When completed, the camera was the largest ever built for astronomical purposes, gathering data at the rate of 37 gigabytes per hour.
On nights with moonshine or mild cloud cover, the imaging camera is replaced with a pair of spectrographs (built by Alan Uomoto and his team at The Johns Hopkins University). They use optical fibers to obtain spectra (and thus redhsifts) of 608 objects at a time. Unlike traditional telescopes in which nights are parceled out among many astronomers carrying out a range of scientific programs, the special-purpose 2.5m SDSS telescope at Apache Point Observatory in New Mexico is devoted solely to this survey, to operate every clear night for five years.
The first public data release from the SDSS, called DR1, contained about 15 million galaxies, with redshift distance measurements for more than 100,000 of them. All measurements used in the findings reported here would be part of the second data release, DR2, which will be made available to the astronomical community in early 2004.
Strauss said the SDSS is approaching the halfway point in its goal of measuring one million galaxy and quasar redshifts.
"The real excitement here is that disparate lines of evidence from the cosmic microwave background (CMB), large-scale structure and other cosmological observations are all giving us a consistent picture of a Universe dominated by dark energy and dark matter", said Kevork Abazajian of the Fermi National Accelerator Laboratory and the Los Alamos National Laboratory.
(A complete list of authors and institutions can be found at www.sdss.org) ILLUSTRATIONS: http://www.hep.upenn.edu/~max/sdss/release.htmlShining as brightly as a million trillion suns yet seldom lasting even one minute, gamma-ray bursts (GRBs) were a great astronomical mystery only recently solved when they were conclusively shown to be linked to cataclysmic explosions called supernovae that mark the deaths of very massive stars.
Gamma-ray bursts come to us--across billions of light years of space and hence billions of years of time--from wholly random directions of the sky about once a day, but astronomers have long suspected they see only a small portion of the total number actually occurring. Until the recent gamma-ray burst/supernova link was made, proving this or even deriving a number of "actual-to-observed" bursts based on observations was exceedingly difficult.
With this link established, two scientists at MIT's Laser Interferometer Gravitational Wave Observatory (LIGO) have just derived an "actual-to-observed" ratio of 450-1. That is, there are roughly 450 GRBs occurring in the observable universe for every one that's detectable by orbiting satellites designed to look for them. This is a figure that not only utilizes the GRB-supernova link but also agrees well with a previous, independently derived ratio that did not use such a link.
These findings could have important consequences in the long hunt for elusive gravitational waves--tiny ripples in space-time predicted by Einstein's theory of general relativity but as yet never directly observed.
"Our 450-1 figure closely agrees with a 500-1 ratio derived in 2001 by other scientists, which makes us more confident in these results," said Maurice van Putten, assistant professor of applied mathematics. Van Putten collaborated with post-doctoral researcher Tania Regimbau in the study. "The earlier figure was based on a method totally independent of the supernova association involving spectral characteristics of the gamma-ray emissions themselves."
To derive their figure, van Putten and Regimbau assumed the now-standard "collapsar" model of GRBs. In that model, the core of an especially massive star undergoes a gravitational collapse (likely resulting in a black hole), producing a massive pressure wave that blasts out of the star in a particular direction. The blast wave collides with dust and gas in the surrounding interstellar medium at velocities near that of light, producing gamma-ray emissions. The type of star used in the collapsar model is also the type of star that ends its life in a supernova.
What astronomers saw in the spectral analysis of the light curves was the unmistakable signature of a supernova, including the presence of oxygen emission lines excited in the blast. This information provided powerful support to a previous, even closer blast on April 25, 1998 that had provided a less conclusive link between supernovae and GRBs.
Once the GRB-supernovae link was established, van Putten and Regimbau used a "very precious" sample of 33 GRBs whose distances (unlike most) are well known, to establish a mathematical relationship between how bright a given burst is and the rate at which the massive stars form and die.
They could do this because the massive stars involved in GRBs and supernovae live for only a few tens of millions of years, as opposed to billions of years. This fact, van Putten said, means such "massive stars essentially die at their place of birth."
One aspect of the collapsar model is that the burst (which precedes the actual supernova explosion) occurs along a particular axis in both directions, as opposed to a symmetric, radial one. Since axes of stars are oriented randomly throughout the universe, we detect only those bursts along or near whose axis the Earth happens to lie.
This effect is known as "beaming" and it means the angle through which the blast of energy is seen is relatively small for most observed blasts--no more than a few degrees of sky. Van Putten said this "beaming" effect is factored into their figure because the relationship is based on peak brightness.
Van Putten said knowing a ratio of actual to observed GRBs will help LIGO precisely because most GRBs are so distant that their gravitational waves won't be detectable by this array. Instead, the findings will give astronomers a sense of how often to expect a detectable gravitational wave produced by a sufficiently close GRB.
"This is an important finding for LIGO because these findings can give us a good handle on the local gravitational-wave event rate. It doesn't matter if the burst is beamed toward us or not because the gravitational wave energy is not beamed," van Putten said.
"Given what LIGO is capable of seeing, and using our results, we would expect an event rate of perhaps one per year, as opposed to one in 450 years, which would be hopeless," he said.
George R. Ricker, principal investigator for the MIT-run High Energy Transient Explorer (HETE2) satellite, hailed the findings as just the kind of success for which he and his colleagues had hoped.
"The HETE mission is rapidly transforming GRBs from vague cosmic mysteries into incisive cosmological probes. This new work is exactly the kind of stimulating research which we dreamed HETE's success would bring about," Ricker said.Space Telescope Science Institute Press Release, April 9, 2002
Someday our Milky Way Galaxy and the neighboring Andromeda Galaxy may come crashing together in a horrendous collision that will twist and distort their shapes beyond recognition. Of course, to see that, you'll have to wait several billion years. But thanks to a combination of research science, Hollywood computer graphics, and large-scale, "immersive" visualization, visitors to the Smithsonian Institution's National Air and Space Museum in Washington, DC, can witness such an event today.
The Space Telescope Science Institute (STScI) in Baltimore, MD, the scientific home of NASA's Hubble Space Telescope, is extending its tradition of stunning imagery by creating a spectacular scientific visualization of two galaxies colliding. This incredibly detailed and immersive, full-dome video sequence will be a highlight of "Infinity Express: A 20-Minute Tour of the Universe," the inaugural show in the National Air and Space Museum's newly renovated Einstein Planetarium, opening Saturday, April 13, 2002.
The scientific visualization by Dr. Frank Summers, an astrophysicist in STScI's Office of Public Outreach, depicts a tremendous collision of two spiral galaxies. Because such events take hundreds of millions of years to occur, researchers use supercomputer simulations to study how galaxies are transformed and merge together. Dr. Summers has taken research data provided by Dr. Chris Mihos (Case Western Reserve University) and Dr. Lars Hernquist (Harvard University), and visualized it using the same software that Hollywood uses to produce blockbuster visual effects.
The result brings astrophysics out of the academic setting and presents a scientifically correct, yet compellingly beautiful animation directly to the planetarium audience. "By combining research simulations with Hollywood visualization techniques, we can create animations that are both accurate and artistic, while visually communicating complex astronomical events and ideas to the public," says Dr. Summers.
This contribution to the National Air and Space Museum marks the first release of scientific visualizations for full-dome video planetariums from the Informal Science Education Group at STScI. While Hubble images are a mainstay of planetarium shows, full-dome scientific visualizations represent a new level of astronomy outreach.
"NASA imagery will greatly benefit this emerging planetarium technology, and we can provide high-quality, dynamic content backed by the expertise of Hubble astronomers," says John Stoke, manager of Informal Science Education at STScI. Going forward, his group will distribute this galaxy collision sequence and other full-dome scientific visualizations, free of charge, to planetariums and show producers across the country and around the world.
Planetariums have entered a new era of full-dome digital video that immerses the viewer in the dynamic wonders of the universe. The video, projected across the entire hemisphere of a planetarium dome, has up to 23 times the resolution of a standard television and is wrapped 360 degrees around the audience, surrounding them in the experience.
While such systems are generally only in the larger planetariums today, technological advances are bringing the capability for full-dome video to thousands of smaller planetariums in the next couple of years. Worldwide, 100 million people visit planetariums every year.
Additional information is available on the Internet at:
http://oposite.stsci.edu/pubinfo/pr/2002/09 and via links in
http://oposite.stsci.edu/pubinfo/latest.html
http://oposite.stscie.du/pubinfo/pictures.html
http://hubblesite.org/go/news and
http://www.nasm.si.edu/nasm/planetarium/
The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA). This work is partially supported by the National Science Foundation through the National Computational Science Alliance and the Partnerships for Advanced Computational Infrastructure. The National Air and Space Museum is owned and operated by the Smithsonian Institution.
STScI PRESS RELEASE NO.: STScI-PR02-08, March 21
Journey to the deepest regions of space and wrestle with the cosmic giants called galaxies.
In "Galaxy Hunter," students can go online and use actual data from NASA's Hubble Space Telescope to study galaxies in deep space. Produced by the formal education team at the Space Telescope Science Institute in Baltimore, Md., the interdisciplinary, Web-based lesson blends astronomy and math skills. A team of scientists, teachers, artists, and Web programmers developed the interactive lesson to bring the results of cutting-edge astronomical observations into the classroom. "Galaxy Hunter" is on the Amazing Space Website [amazing-space.stsci.edu]. Amazing Space is a group of Web-based, interactive activities primarily designed for classroom use, from kindergarten through twelfth grade.
The galaxies that students examine in "Galaxy Hunter" are part of the Hubble "Deep Fields," the Hubble telescope's clearest, most distant views of the universe ever obtained. Gazing billions of years back in time, the Earth-orbiting observatory uncovered a bewildering assortment of galaxies in various stages of evolution.
Scientists used mathematics to unlock many galactic secrets hidden in the two deep fields. Now students can analyze the same faraway galaxies that dazzled astronomers and sample the types of galaxies found in the deep views. Then they can compare their samples with those of astronomers to determine whether the galaxies in the two deep fields are similar. Along the way, they'll learn about bias in sampling techniques and the role of sample variability in determining the optimal sample size. Based on their sample analysis, students will try to answer the same question as the astronomers who observed the deep fields: Does the universe look the same in the two Hubble deep fields? Scientists believe that the universe generally looks the same in all directions.
The lesson also includes a teacher guide that helps prepare educators to present the lesson in the classroom. In the guide, teachers will find "science background" information, which explains the galaxy types, the galaxy classification system, and how astronomers selected the Hubble deep fields. The lesson also adheres to the National Education Standards for grades 9 to 12.
When students are finished hunting for galaxies, they can try unscrambling the schedule for a Hubble telescope servicing mission. Although the Hubble telescope's Servicing Mission 3B is over, students can still play the role of a NASA scientist who plans the Hubble servicing missions. In "Be the Mastermind Behind the Mission," another online, interactive activity, students attempt to fix a mixed up order of events for the Hubble servicing mission. Their job is to place the schedule of servicing mission events, which includes spacewalks and the launch of the space shuttle, in proper order. The interdisciplinary lesson focuses on reading and technology skills, and is aimed at sixth-through eighth-graders.
"Galaxy Hunter" and "Be the Mastermind Behind the Mission" are
available on the Amazing Space website at:
http://amazing-space.stsci.edu/ghunter
http://amazing-space.stsci.edu/mastermind
On January 14, 2000, a team of astronomers using NASA's Chandra X-ray Observatory announced the discovery of an unusual source very near the nucleus of the Andromeda Galaxy, also known as M31. The proximity of this source to the nucleus, and its extraordinarily low temperature relative to other X-ray sources in M31, led the astronomers to associate it with the supermassive black hole located at the center of M31. These results were extraordinary because they could not be explained by the standard models developed for supermassive black holes in galaxies like the Milky Way and Andromeda. However, recent observations with NASA's Hubble Space Telescope and analysis of additional Chandra observations of M31 by the same team have shown that this association was in error.
The team, led by Michael Garcia of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., has recently detected two X-ray emitting globular star clusters -- so called because of their spherical shape -- in the vicinity of the M31 supermassive black hole. The globular clusters, which are visible on both Hubble and Chandra images, can be used as a cross-check to determine the position of all of the X-ray sources near the supermassive black hole to an accuracy ten times greater than before.
These new and slightly revised positions show that the very cool X-ray source is actually located approximately 1 arcsecond south of the supermassive black hole. A second, hotter X-ray source, is found to have a location that is consistent with the position of the super-massive black hole, but the astronomers caution that, due to the complex nature of the region, it is not possible at this time to say with certainty that this source is due to the supermassive black hole.
See
http://chandra.harvard.edu/photo/cycle1/0007rev/index.html
[The object colored blue visible on the photo in the text is no longer thought to be the black hole. jmp]
Chandra X-ray Observatory Center Press Release
NASA's Chandra X-ray Observatory has captured a stunning image of Centaurus A, a massive elliptical galaxy approximately 11 million light years from Earth. In addition to the bright central source, a suspected supermassive black hole, and the X-ray jet emanating from the core, more than 200 point-like X-ray sources were identified and studied. Because of their distribution around the center of the galaxy, it is believed that most of these point-like X-ray sources are X-ray binaries in which a neutron star or stellar-sized black hole is consuming matter from a nearby companion star. A diffuse cloud of hot X-ray producing gas that envelopes the central region can also be seen. A team of scientists, led by Ralph Kraft of the Smithsonian Astrophysical Observatory, has begun to study each of these components of X-ray emission from Cen A. The unprecedented imaging resolution of Chandra allows scientists for the first time to clearly resolve each of these distinct components of the X-ray emission for detailed study. This latest image of Centaurus A was the result of approximately 20 hours of observations with Chandra's Advanced CCD Imaging Spectrometer on December 5, 1999, and May 17, 2000.
The image and other information associated with this release are
available at:
http://chandra.harvard.edu
and
http://chandra.nasa.gov
You can watch simulations of galaxy simulations, control their rate, and control the viewing angle with this CD-ROM. See http://www.virtualstar.co.uk