Posted on by Fraser Cain

A Dozen New Planets Discovered

The past four weeks have been heady ones in the planet-finding world: Three teams of astronomers announced the discovery of 12 previously unknown worlds, bringing the total count of planets outside our solar system to 145.

Just a decade ago, scientists knew of only the nine planets – those in our local solar system. In 1995, improved detection techniques produced the first solid evidence of a planet circling another star. A proliferation of discoveries followed, and now dozens of ongoing search efforts around the globe add steadily to the roster of worlds. Most of these planets differ markedly from the planets in our own solar system. They are more similar to Jupiter or Saturn than to Earth, and are considered unlikely to support life as we know it.

The news of the past four weeks has included:

* The discovery of six new gas-giant planets by two teams of European planet-hunters was announced this week. Two of these planets are similar in mass to Saturn; three belong to a class known as “hot jupiters” because of their close proximity to the host stars. The sixth is a gas giant at least four-and-a-half times the mass of Jupiter.

All were discovered as part of the High Accuracy Radial velocity Planet Search (HARPS), an ongoing search program based at La Silla Observatory in Chile.

* On January 20, a paper posted in the online edition of the Astrophysical Journal described five new gas-giant type planets detected by a team of U.S. astronomers. These planets provide further statistical information about the distribution and properties of planetary systems, according to the paper.

The U.S. team based its finding on observations obtained at the W.M. Keck Observatory in Hawaii, which is jointly operated by the University of California and Caltech. Observation time was granted by both NASA and the University of California.

* Last week, Penn State’s Alex Wolszczan and Caltech’s Maciej Konacki announced the discovery of the smallest planet-like body detected beyond our solar system. The object belongs to a strange class known as “pulsar planets.” It is about one-fifth the size of Pluto and orbits a rapidly spinning neutron star, called a pulsar.

A pulsar is a dense and compact star that forms from the collapsing core left over from the death of a massive star. The new pulsar planet is the fourth to be discovered; all orbit the same pulsar, named PSR B1257+12.

Because the planets around the pulsar are continually strafed by high-energy radiation, they are considered extremely inhospitable to life. (Note: The current planet count posted on this website includes only planets around normal stars.)

Two methods of detection
The pulsar planet was discovered by observing the neutron star’s pulse arrival times, called pulsar timing. Variations in these pulses give astronomers an extremely precise method for detecting the phenomena that occur within a pulsar’s environment.

The gas-giant planets were detected using the radial velocity method, which infers the presence of an unseen companion because of the back-and-forth movement induced in the host star. This movement is detectable as a periodic red shift and blue shift in the star’s spectral lines. (For more about this method, see the article Finding Planets.)

The names of the new planets around main sequence stars are:

* HD 2638 b
* HD 27894 b
* HD 63454 b
* HD 102117 b
* HD 93083 b
* HD 142022A b
* HD 45350 b
* HD 99492 b
* HD 117207 b
* HD 183263 b
* HD 188015 b

Original Source: NASA Astrobiology Report

Posted on by Fraser Cain

Signs of Underground Life on Mars

NASA researchers believe they’ve found strong evidence that there could be underground life on Mars, huddled around pockets of liquid water. They haven’t found the life directly, but instead have discovered a unique methane signature that matches similar environments here on Earth, such as subsurface areas around Rio Tinto, a red-stained river in Spain. In order to get confirmation, NASA would need to send a spacecraft to Mars capable of drilling into the ground – unfortunately, none are planned currently.

Posted on by Fraser Cain

Close Up on Enceladus

This image was taken during Cassini’s first close approach to Enceladus.

The image was taken on February 17, 2005 in visible light with the narrow angle camera from a distance of approximately 10,750 kilometers (6,680 miles). Resolution in the image is 60 meters (197 feet) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: NASA/JPL/SSI Release

Posted on by Fraser Cain

Galaxy Clusters Formed Early

Image credit: Subaru Telescope
Galaxies often congregate to form clusters of galaxies. At the present day, clusters have tens and hundreds of member galaxies and are the largest astronomical objects in the Universe. Knowing how they formed is a key to understanding the past and future of the Universe.

To study how the Universe has changed over large scales in space and time, it is essential to observe deeply a wide area of the sky. A large number of researchers are now studying the Subaru-XMM Deep Survey Field (SXDS), an approximately one square degree area of the sky in the direction of the constellation Cetus, the Whale, at many wavelengths using several telescopes. (Note 1)

To understand the origin of galaxy clusters, Masami Ouchi, currently at the Space Telescope Science Institute, decided to study how galaxies approximately 12.7 billion light years away (a red shift of 5.7) were distributed in the SXDS. By using the color of galaxies as a guide to their distance, Ouchi and his collaborators found 515 galaxies in a volume 500 million light years in height and width and 100 million light years in depth in images from Subaru’s prime focus camera (Suprime-Cam). (Note 2)

Figure 1 shows a density map of the galaxies in this volume as seen on the sky. This map represents the physical structures in the Universe at the farthest distances and the earliest times that astronomers have been able to observe to date. The yellow regions are where there are the highest concentration of galaxies. (Note 3)

In the bottom portion of this map, the researchers found a concentration of galaxies that could not be explained by chance. By obtaining accurate distance estimates to these galaxies using Subaru’s Faint Object Camera and Spectrograph (FOCAS), the researchers confirmed that there were six galaxies concentrated in a small volume only 3 million light years in diameter, forming a galaxy cluster. Figure 2 identifies the six member galaxies of the cluster.

The cluster has several properties that reveal its young age. It is one hundred times less massive than present day galaxy clusters and has significantly fewer members. Moreover, its member galaxies are producing stars at one hundred times the rate of galaxies outside the cluster.

The infant galaxy cluster existed at a time when the Universe was only one billion years old. The youngest portraits of galaxy clusters that astronomers previously had were from the Universe at an age of one and a half billion years. As any parent would attest, young children change rapidly. The portrait of a galaxy cluster at a younger age fills a significant gap in our knowledge of the early history of the Universe when stars, galaxies, and clusters were first forming.

“The fact that a cluster is already forming so soon after the Big Bang puts strong constraints on the fundamental structure of the Universe”, says Ouchi. The prevailing theory of cosmology postulates that smaller mass structures form first and then grow into more massive structures. “Our results seem to contradict the prevailing wisdom, but the real challenge is in understanding how well the distribution of visible matter such as galaxies correlates with the distribution of mass in general. As we continue to fill in the gaps in the early history of clusters, we should be able to resolve such ambiguities”, he says.

These results were published in the February 10, 2005, edition of the Astrophysical Journal (ApJ 620, L1-L4) and will be presented at the meeting “The Future of cosmology with clusters of Galaxies” beginning on February 26, 2005, in Waikoloa, Hawaii.

Note 1: For more information on the Subaru/XMM-Newton Deep Survey field, see the June 2004 press release on the SXDS public data release and the SXDS home page.

Note 2 : For more information on how astronomers use colors to look for distant galaxies see the March 2003 press release on the discovery of one the most distant galaxies currently known.

Note 3: Maps of the cosmic microwave background such as those from COBE or WMAP show the unevenness in the heat left over from the Big Bang that eventually led to the physical structures revealed in the new map.

Original Source: Subaru Telescope News Release

Posted on by Fraser Cain

Saturn’s Mysterious Auroras Explained

Scientists studying data from NASA’s Cassini spacecraft and Hubble Space Telescope have found that Saturn’s auroras behave differently than scientists have believed for the last 25 years.

The researchers, led by John Clarke of Boston University, found the planet’s auroras, long thought of as a cross between those of Earth and Jupiter, are fundamentally unlike those observed on either of the other two planets. The team analyzing Cassini data includes Dr. Frank Crary, a research scientist at Southwest Research Institute in San Antonio, Texas, and Dr. William Kurth, a research scientist at the University of Iowa, Iowa City.

Hubble snapped ultraviolet pictures of Saturn’s auroras over several weeks, while Cassini’s radio and plasma wave science instrument recorded the boost in radio emissions from the same regions, and the Cassini plasma spectrometer and magnetometer instruments measured the intensity of the aurora with the pressure of the solar wind. These sets of measurements were combined to yield the most accurate glimpse yet of Saturn’s auroras and the role of the solar wind in generating them. The results will be published in the February 17 issue of the journal Nature.

The findings show that Saturn’s auroras vary from day to day, as they do on Earth, moving around on some days and remaining stationary on others. But compared to Earth, where dramatic brightening of the auroras lasts only about 10 minutes, Saturn’s can last for days.

The observations also show that the Sun’s magnetic field and solar wind may play a much larger role in Saturn’s auroras than previously suspected. Hubble images show that auroras sometimes stay still as the planet rotates beneath, like on Earth, but also show that the auroras sometimes move along with Saturn as it spins on its axis, like on Jupiter. This difference suggests that Saturn’s auroras are driven in an unexpected manner by the Sun’s magnetic field and the solar wind, not by the direction of the solar wind’s magnetic field.

“Both Earth’s and Saturn’s auroras are driven by shock waves in the solar wind and induced electric fields,” said Crary. “One big surprise was that the magnetic field imbedded in the solar wind plays a smaller role at Saturn.”

At Earth, when the solar wind’s magnetic field points southward (opposite to the direction of the Earth’s magnetic field), the magnetic fields partially cancel out, and the magnetosphere is “open”. This lets the solar wind pressure and electric fields in, and allows them to have a strong effect on the aurora. If the solar wind’s magnetic field isn’t southward, the magnetosphere is “closed” and solar wind pressure and electric fields can’t get in. “Near Saturn, we saw a solar wind magnetic field that was never strongly north or south. The direction of the solar wind magnetic field didn’t have much effect on the aurora. Despite this, the solar wind pressure and electric field were still strongly affecting auroral activity,” added Crary. Seen from space, an aurora appears as a ring of energy circling a planet’s polar region. Auroral displays are spurred when charged particles in space interact with a planet’s magnetosphere and stream into the upper atmosphere. Collisions with atoms and molecules produce flashes of radiant energy in the form of light. Radio waves are generated by electrons as they fall toward the planet.

The team observed that even though Saturn’s auroras do share characteristics with the other planets, they are fundamentally unlike those on either Earth or Jupiter. When Saturn’s auroras become brighter and thus more powerful, the ring of energy encircling the pole shrinks in diameter. At Saturn, unlike either of the other two planets, auroras become brighter on the day-night boundary of the planet which is also where magnetic storms increase in intensity. At certain times, Saturn’s auroral ring is more like a spiral, its ends not connected as the magnetic storm circles the pole.

The new results do show some similarities between Saturn’s and Earth’s auroras: Radio waves appear to be tied to the brightest auroral spots. “We know that at Earth, similar radio waves come from bright auroral arcs, and the same appears to be true at Saturn,” said Kurth. “This similarity tells us that, on the smallest scales, the physics that generate these radio waves are just like what goes on at Earth, in spite of the differences in the location and behavior of the aurora.”

Now with Cassini in orbit around Saturn, the team will be able to take a more direct look at the how the planet’s auroras are generated. They will next probe how the Sun’s magnetic field may fuel Saturn’s auroras and learn more details about what role the solar wind may play. Understanding Saturn’s magnetosphere is one of the major science goals of the Cassini mission.

For the latest images and information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

The Cassini-Huygens mission is a cooperative mission of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Office of Space Science, Washington, D.C.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Giant Crater Discovered on Titan

A giant impact crater the size of Iowa was spotted on Saturn’s moon Titan by NASA’s Cassini radar instrument during Tuesday’s Titan flyby.

Cassini flew within 1,577 kilometers (980 miles) of Titan’s surface and its radar instrument took detailed images of the surface. This is the third close Titan flyby of the mission, which began in July 2004, and only the second time the radar instrument has examined Titan. Scientists see some things that look familiar, along with scenes that are completely new.

The new radar images are available at: http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

“It’s reassuring to look at two parts of Titan and see similar things,” said Dr. Jonathan Lunine, Cassini interdisciplinary scientist from the University of Arizona, Tucson. “At the same time, there are new and strange things.”

This flyby is the first time that Cassini’s radar and the imaging camera overlapped. This overlap in coverage should be able to provide more information about the surface features than either technique alone. The 440-kilometer-wide (273-mile) crater identified by the radar instrument was seen before with Cassini’s imaging cameras, but not in this detail.

A second radar image released today shows features nicknamed “cat scratches”. These parallel linear features are intriguing, and may be formed by winds, like sand dunes, or by other geological processes.

On Thursday, Cassini will conduct its first close flyby of Saturn’s icy moon Enceladus (en-SELL-uh-duss) at a distance of approximately 1,180 kilometers (730 miles). Enceladus is one of the most reflective objects in the solar system, so bright that its surface resembles freshly fallen snow. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA’s Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

What Telescope is Right for You?

Image credit: Astro.Geekjoy
Contrary to what might be expected, it’s actually quite easy to select a telescope, followed by another telescope, followed by another. In fact many amateurs have been known to select dozens.

But here’s the real challenge: Try selecting your last telescope first. To do so comes down to just two things: Views and usability. If a scope doesn’t deliver the views, you won’t use it. And if it isn’t usable, you won’t bother with the views. It’s as simple – and as difficult – as that.

For instance, a very compact telescope on a lightweight mount can easily be transported from house to yard and back again. If it fails to show you anything you want to see however, the instrument will quickly become a “conversation piece” – like that brass telescope in the office at work…

Meanwhile a large telescope may require complex setup and dissassembly – not to mention the brute force needed to carry around as parts. Such a scope – despite bright views – may be rendered useless for lack of spontaneous access. But other reasons can also discourage the observer – such as difficulty orienting a large instrument toward certain regions of the sky or having to stand on a pedestal or ladder to engage the eyepiece. Great views – once you bother to set it all up…

The author has used scopes at both these extremes. One telescope of fine optics gave sharp views but – due to extremely small aperture – was unable to show anything worth viewing. (Despite the fact that the entire assembly – scope AND mount – could easily be carried about in one hand.) Meanwhile the author has also watched fellow observers take nearly an hour setting up a large truss-framed Newtonian telescope on a relatively simple (dobsonian) mount. (All the while the sky darkened and stars drifted a full fifteen degrees across the heavens.) Of course once this particular scope was assembled, the author was more than willing to peek through the eyepiece. So setup time and portability are important factors the thoughtful amateur may want to consider when evaluating telescope types and models for purchase and personal use.

Another important issue to consider is observing position. After long hours on the feet you may not prefer to stand equally long hours observing. Additionally, even slight shifts in balance can complicate seeing fine planetary detail or resolving ultra-close double stars. Of course, measures can be taken to offset ergonomic problems such as these, comfortable observing stands and chairs are available from various suppliers. So if you find yourself spending less time at the eyepiece than you might pay some attention to your body and seek out a workable after-market solution.

But ultimately the telescope you want follows from the type celestial studies you prefer to view. And that, of course, has a lot to do with the kind of conditions you observe through. (Ranging from dark rural skies through well-lit city sidewalks.) But it also has to do with the conditions you observe from. (Inside you, the stuff of your own head – and heart…)

The faintest studies visible in amateur telescopes are of a class known as quasars. These objects are extremely remote and – despite their incredible intrinsic luminosity – are very faint. Like most quasars, the brightest – 3C273 varies in brightness but at peak output (when its supermassive black hole core is about to swallow some star or another) it appears as a faint star of the 13th magnitude. To make a study of the dozen or so quasars accessible through amateur telescopes requires all the aperture possible. (Scopes to thirty inches in aperture are available from manufacturers.) An interest in quasars would place you on the very edge of what is visually possible in amateur astronomy.

In contrast to quasars, the brightest celestial study is the Sun. Due to its brilliance, it takes but a few inches of aperture to get decent views of spots, faculae, granularities, and other fine features. (The Sun is so intense that direct inspection without a solar filter will permanently damage the retina!!!) Solar observing is best pursued with small scopes due to the reality of daylight sky conditions. As the Sun heats the atmosphere, super-fine detail is lost. Because of this, three inch instruments deliver all detail possible (except when observing at high elevations). Solar observing can lead to the purchase of some very expensive accessories. (Super narrow band hydrogen alpha filters can reveal prominences even as they leap off Sol’s limb.) Conceivably you could spend tens of thousands of US dollars putting together the high-precision optics needed to mask the Sun and view the corona as well! But in general – due to the low cost of solar rejection filters and small apertures involved – beginning solar observation is an inexpensive alternative for those astronomers who prefer sleep to late night skies.

Quasars and solar observation mark the two extremes of aperture in scope selection. We might call this the “light-gathering axis”. This is the axis most people think of when considering a scope. But there are other extremes to consider as well…

Very slow telescopes (those with focal lengths greater than twelve times greater than aperture-F12+) are limited in terms of how much of the sky they can show in a single field of view. To specialize in observing extended star fields (M24 in Sagittarius for instance) or nebulosity (the North America Nebula) three plus degree fields are desirable. For this reason small scopes of low – but quite usable magnification (20-30x) – with fine flat fields – make excellent choices. Such scopes are pretty much limited to fast achromatic or apochromatic refractors, or Maksutov-Newtonian models of five inches or less aperture. (Although fast newtonian models are available, such scopes often show pronounced coma at wide angles. In general, scopes that include light-handling refractory collector elements (refractors, Maksutovs and Schmidt’s) give superior off-axis image quality to all but the slowest pure reflector models.

Meanwhile some very fast scopes (F7-) can lack the kind of optical quality needed to specialize in lunar-planetary-double star observing. In such cases, scopes of greater focal ratios (F10+) are preferred. However even these slower scopes require well-corrected optics. Because of high power use, lunar-planetary telescopes ride best on stable mounts able to track against the Earth’s rotation. Such scopes also need enough aperture (four inches or greater) to resolve fine detail or distinguish close stars – especially those of widely dissimilar magnitudes. Outfitting scopes of this type is often quite expensive (several to many thousands of US dollars). But despite the cost, these instruments have great appeal to a very discriminating subset of amateurs – “optophiles” – those who prize sharp, high contrast views – even though appreciably “dimmer” compared to much larger and often far-less expensive instruments.

So with this we’ve explored the limits of the “image-scale” axis. At one extreme are scopes that deliver large flat fields ignoring fine structure, and at the other those with small fields of view providing exceedingly fine gradations of low-contrast detail. On one hand context is king and on the other subtlety is found in the details.

Most observers find that their interests lie between the extremes. An observer may want to take in as much of a faint extended study as possible, while also boosting magnification to glean fine details as well. Such observers are interested in views that include the entire Great Nebula in Orion, while also being able to distinctly reveal gradations visible in Saturn’s ring system. The reality is that such scopes are not likely to take in the entire Cygnus Loop as a single field of view but they should resolve numerous components in the Great Hercules Cluster. For intermediate observations of this type, magnifications ranging from 50 to 200x are needed – a range that doesn’t necessarily require a tracking mount but can keep you busy without one. Meanwhile enough light must be gathered to reveal faint structure.

What’s the best scope1 for you?

Perhaps its the one that gets you out week after week exploring the Moon, planets, doubles, clusters, nebulae, or galaxies until you have no choice but to get another – along with the observatory to house it in!

1 The author has found that the Greek aphorism “Know Thyself” is at root of most matters of choice, taste, and aspiration. Selecting an appropriate instrument is a voyage of self-discovery. Enjoy the journey!

About The Author:
Inspired by the early 1900’s masterpiece: “The Sky Through Three, Four, and Five Inch Telescopes”, Jeff Barbour got a start in astronomy and space science at the age of seven. Currently Jeff devotes much of his time observing the heavens and maintaining the website Astro.Geekjoy.

Posted on by Fraser Cain

Titan’s Fourth Flyby

This image was taken during Cassini’s third close approach to Titan on Feb. 15, 2005.

The image was taken with the Cassini spacecraft narrow angle camera, through a filter sensitive to wavelengths of polarized infrared light, centered at 938 nanometers.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . For additional images visit the Cassini imaging team homepage http://ciclops.org.

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

SMART-1’s Mission Extended

Illustration credit: ESA
ESA’s SMART-1 mission was extended by one year, pushing back the mission end date from August 2005 to August 2006.

ESA’s Science Programme Committee endorsed unanimously the proposed one-year extension of SMART-1 on 10 February 2005.

The extension by one year of the mission will provide opportunities to extend the global coverage, compared to the original six-month mission, and to map both southern and northern hemispheres at high resolution. The new orbit will also be more stable and require less fuel for maintenance.

The extension also gives the possibility to perform detailed studies of areas of interest by performing stereo measurements for deriving topography, multi-angle observations for studying the surface ‘regolith’ texture, and mapping potential landing sites for future missions.

Implementation of this mission extension will be in two periods of six months that correspond to different orbital parameters and illumination conditions. During the first period, the southern survey study is to be completed and dedicated pointings made for multi-angle, stereo and polar illumination studies.

In the second period, high-resolution coverage of the Moon on the equator and part of the northern hemisphere will take place due to the favourable illumination conditions. High resolution follow-up observations of specific targets will also be made, as well as observations relevant for the preparation of future international lunar exploration missions.

Between 10 January and 9 February, SMART-1’s electric propulsion system (or ‘ion engine’) was not active. This allowed mission controllers to accurately determine the amount of fuel remaining, as well as ensure accurate planning for a mission extension, and obtain reconnaissance data from an orbit at 1000-4500 kilometres above the lunar surface.

All the instruments have been performing well from this orbit. As the ion engine is now active again, SMART-1 will spiral down to arrive at the lunar science orbit by the end of February.

The cruise and lunar approach has permitted the demonstration of a number of technologies, such as spacecraft, navigation, operations and instruments, which will be useful for future missions. The SMART-1 mission has now fulfilled its primary objective ? to demonstrate the viability of solar electric propulsion, or ‘ion drives’.

Original Source: ESA News Release

Posted on by Fraser Cain

The Limit of Black Holes

The very largest black holes reach a certain point and then grow no more, according to the best survey to date of black holes made with NASA’s Chandra X-ray Observatory. Scientists have also discovered many previously hidden black holes that are well below their weight limit.

These new results corroborate recent theoretical work about how black holes and galaxies grow. The biggest black holes, those with at least 100 million times the mass of the Sun, ate voraciously during the early Universe. Nearly all of them ran out of ‘food’ billions of years ago and went onto a forced starvation diet.

Focus on Black Holes in the Chandra Deep Field North Focus on Black Holes in the Chandra Deep Field North
On the other hand, black holes between about 10 and 100 million solar masses followed a more controlled eating plan. Because they took smaller portions of their meals of gas and dust, they continue growing today.

“Our data show that some supermassive black holes seem to binge, while others prefer to graze”, said Amy Barger of the University of Wisconsin in Madison and the University of Hawaii, lead author of the paper describing the results in the latest issue of The Astronomical Journal (Feb 2005). “We now understand better than ever before how supermassive black holes grow.”

One revelation is that there is a strong connection between the growth of black holes and the birth of stars. Previously, astronomers had done careful studies of the birthrate of stars in galaxies, but didn’t know as much about the black holes at their centers.

“These galaxies lose material into their central black holes at the same time that they make their stars,” said Barger. “So whatever mechanism governs star formation in galaxies also governs black hole growth.”

Astronomers have made an accurate census of both the biggest, active black holes in the distance, and the relatively smaller, calmer ones closer by. Now, for the first time, the ones in between have been counted properly.

Growth of the Biggest Black Holes Illustrated Growth of the Biggest Black Holes Illustrated
“We need to have an accurate head count over time of all growing black holes if we ever hope to understand their habits, so to speak,” co-author Richard Mushotzky of NASA’s Goddard Space Flight Center in Greenbelt, Md.

Supermassive black holes themselves are invisible, but heated gas around them — some of which will eventually fall into the black hole – produces copious amounts of radiation in the centers of galaxies as the black holes grow.

This study relied on the deepest X-ray images ever obtained, the Chandra Deep Fields North and South, plus a key wider-area survey of an area called the “Lockman Hole”. The distances to the X-ray sources were determined by optical spectroscopic follow-up at the Keck 10-meter telescope on Mauna Kea in Hawaii, and show the black holes range from less than a billion to 12 billion light years away.

Since X-rays can penetrate the gas and dust that block optical and ultraviolet emission, the very long-exposure X-ray images are crucial to find black holes that otherwise would go unnoticed.

Chandra found that many of the black holes smaller than about 100 million Suns are buried under large amounts of dust and gas, which prevents detection of the optical light from the heated material near the black hole. The X-rays are more energetic and are able to burrow through this dust and gas. However, the largest of the black holes show little sign of obscuration by dust or gas. In a form of weight self-control, powerful winds generated by the black hole’s feeding frenzy may have cleared out the remaining dust and gas.

Other aspects of black hole growth were uncovered. For example, the typical size of the galaxies undergoing supermassive black hole formation reduces with cosmic time. Such “cosmic downsizing” was previously observed for galaxies undergoing star formation. These results connect well with the observations of nearby galaxies, which find that the mass of a supermassive black hole is proportional to the mass of the central region of its host galaxy.

The other co-authors on the paper in the February 2005 issue of The Astronomical Journal were Len Cowie, Wei-Hao Wang, and Peter Capak (Institute for Astronomy, Univ. of Hawaii), Yuxuan Yang (GSFC and the Univ. of Maryland, College Park), and Aaron Steffan (Univ. of Wisconsin, Madison).

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA’s Space Mission Directorate, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

Original Source: Chandra News Release