Astronomy Picture of the Day 04-22-04

Explanation: Discovered by the the Lincoln Near Earth Asteroid Research (LINEAR) project in October of 2002, comet C/2002 T7 is now visiting the inner solar system, making its closest approach (see animation by L. Koehn) to the Sun tomorrow, April 23rd. Emerging from the solar glare, the comet is now just visible to the unaided eye in the constellation Pisces, near the eastern horizon in morning twilight. In this gorgeous telescopic view recorded before dawn yesterday, the clearly active comet has developed an extensive, complex tail extending over 2 degrees in the anti-sunward direction, and a pronounced anti-tail or anomalous tail. Later next month this comet should appear brighter, making its closest approach to planet Earth on May 19th. In fact, it could share southern skies with another naked-eye comet, also anticipated to brighten in May, designated C/2001 Q4 (NEAT).

Congressman urges slower approach to new space plan
BY JEFF FOUST
SPACEFLIGHT NOW
Posted: April 21, 2004

An influential member of Congress said Wednesday that he believed NASA should adopt a slower approach to its new space exploration program because of budget concerns.

Rep. Sherwood Boehlert (R-NY). Credit: Jeff Foust

Rep. Sherwood Boehlert (R-NY), chairman of the House Science Committee, said in an address during the AIAA's International Policy Seminar on Capitol Hill in Washington that he agreed with the "broad outlines" of the exploration initiative unveiled by President George W. Bush in January, but was concerned with its cost and schedule.

"The pace at which we move ahead probably will have to be slower than what the President proposed because funds are likely to be more limited than he assumed," Boehlert said.

His concerns stemmed from the ongoing debate over the fiscal year 2005 budget. The president's budget proposal called for a 5.6 percent increase in NASA's budget, to $16.2 billion, to help in part pay for the initial stages of the exploration plan. That increase is among the largest in the proposed budget outside of defense and homeland security; the average domestic "discretionary" program in the budget will see an increase of only half a percent, according to Boehlert.

"In such a budget, should NASA receive almost a six percent increase? Is it the highest domestic spending priority? I don't think so, and I doubt my colleagues will either," he said.

Boehlert also noted that it is unlikely that Congress will pass a budget for NASA - as part of an appropriations bill that also includes money for the Departments of Veterans Affairs and Housing and Urban Development, as well as other independent agencies - by the time the 2005 fiscal year begins this October 1. Boehlert predicted that the budget would not be approved until after Election Day in early November, requiring NASA and other affected agencies to subsist on temporary "continuing resolutions" until a final budget is approved. Those continuing resolutions will not include funding for new programs in the exploration initiative that start in fiscal year 2005.

Boehlert also expresses concern that the proposed NASA budget makes too many cuts in other NASA programs, including space science, earth science, and aeronautics, to provide funding for the exploration initiative. He was particularly concerned about cuts in the earth sciences, including climate change research funded in part by NASA. "Do I think that it's more important to know more about the Earth than it is to know more about Mars?" he asked. "I do, and I don't think it's a close question."

Those issues led Boehlert to conclude that the exploration plan - which calls for completing the space station and retiring the shuttle by 2010, developing a replacement Crew Exploriation Vehicle capable of carrying humans into orbit by 2014, and returning humans to the Moon by 2020 - may need to be slowed down. "How much slower? Slow enough to delay a return to the moon beyond 2020? It's too soon to know that." He added that his staff on the Science Committee is working to draft an alternative version of a 2005 NASA budget that would restore some of the cuts in other programs while allowing exploration efforts to get started.

While critical of the budget and schedule components of the exploration plan, Boehlert indicated that he supported what he called the "broad outlines" of the plan, including retiring the shuttle, sending humans to the Moon, and planning for eventual human missions to Mars. "The president deserves enormous credit for doing what many of us had been calling for: laying out a clear vision for the space program, making tough choices, and providing a plan that does not rely on Apollo-like spikes in spending," Boehlert said.

He cautioned, though, that his enthusiasm for the plan does not necessarily carry over to his colleagues in Congress. "I have no idea of how the Congress would vote right now on any of the notions I just mentioned, although I imagine that most members would be reluctant to simply walk away from the human spaceflight program," he said.

"I think it's fair to say that most members of Congress have not begun to wrestle with these questions, or even to take the space initiative seriously, or to ponder what alternatives there are to the President's proposal," he added. "In broad terms there aren't a lot of palatable alternatives if you want to continue the human space flight program."

Intermediate mass black hole mystery resolved
UNIVERSITY OF AMSTERDAM NEWS RELEASE
Posted: April 19, 2004

New research, funded by the Royal Netherlands Academy of Sciences, the Institute of Advanced Physical and Chemical Research, NASA and the University of Tokyo, solved the mystery of how a black hole, with the mass more than several hundreds times larger than that of our Sun, could be formed in the nearby starburst galaxy, M82.

Chandra X-ray image of the relevant part of M82 with the observed star clusters indicated. The color image is from the 28 October 1999 X-ray observation by Matsumoto et al (2001). The brightest X-ray source (M82 X-1) is near the center of the image. The star clusters are indicated by circles. The positions of the two star clusters MGG-9 and MGG-11 are indicated with squares. The magnified infrared images of these star clusters from McCrady et al (2003) observations are presented in the upper right (MGG-11) and lower left (MGG-9) corners.

Recent observations of the Chandra X-ray observatory (Matsumoto et al., 2001 ApJ 547, L25) indicate the presence of an unusually bright source in the star cluster MGG11 in the starburst galaxy M82. The properties of the X-ray source are best explained by a black hole with a mass of about a thousand times the mass of the Sun, placing it intermediate between the relatively small (stellar mass) black holes in the Milky way Galaxy and the supermassive black holes found in the nuclei of galaxies. For comparison, stellar-mass black holes are only a few times more massive than the Sun, whereas the black hole in the center of the Milky-way Galaxy is more than a few million times more massive than the Sun.

An international team of researchers, using the world's fastest computer, the GRAPE-6 system in Japan, were engaged in a series of simulations of star clusters that resembled MGG11. They used the GRAPE-6 to perform simulations with two independently developed computer programs (Starlab and NBODY4 developed by Sverre Aarseth in Cambridge), both of which give the same qualitative result. The simulations ware initiated by high resolution observations of the star cluster MGG11 by McCrady et al (2003, ApJ 596, 240) using the Hubble Space Telescope and Keck, and by Harashima et al (2001) using the giant Subaru telescope.

Chandra X-ray image of the central region of the starburst galaxy M82.The GRAPE's detailed, star-by-star simulations represent the state of the art in cluster modeling. For the first time using the GRAPE, researchers perform simulations of the evolution of young and dense star clusters with up to 600000 stars; they calculate the orbital trajectory and the evolution of each star individually. Using this unique tool, the team found they could reproduce the observed characteristics of the star cluster MGG11. As a bonus, however, the star cluster produces a black hole with a mass between 800 and 3000 times the mass of the Sun. The black hole is produced within 4 million years which is in an early phase in the evolution of the star cluster. During this phase the stellar density in the center becomes so high that physical collisions between the stars become frequent. If the stellar densities exceed a million times the density in the neighborhood of the Sun, collision start to dominate the further evolution of the star cluster.

In this over-dense cluster center, stars experience repeated collisions with each other, resulting in a collision runaway in which a single stars grows to enormous mass. After the central fuel of this star is exhausted, it collapses to a black hole of about 1000 times the mass of the Sun.

New results of these detailed computer simulations, published in Nature show that the star cluster in which the X-ray source resides has characteristics such that a black hole of 800-3000 times the mass of the Sun can form within a very short time. The calculations therewith provide compelling evidence for the process which produces intermediate mass black holes and at the same time provide an explanation for the bright X-ray source observed in the cluster.

The GRAPE team's members are Simon Portegies Zwart, from the University of Amsterdam in the Netherlands; Holger Baumgardt, from RIKEN in Tokyo; Piet Hut, of the Institute for Advanced Study in Princeton, N.J.; Jun Makino from Tokyo University; Steve McMillan, from Drexel University in Philadelphia.

The GRAPE group's results appear in the April 15, 2004, issue of Nature.

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