Tuesday, September 25, 2007

The mysterious CK Vul

So what did Pere Dom Anthelme and Hevelius see in 1670? See Hajduk et al (astro-ph/0709.3746).

Monday, September 24, 2007

Black hole finding and who killed the Dinosaurs

NASA has approved the restart of NuSTAR, a SMEX level mission, which is a focusing hard X-ray telescope with the primary objectives of "conducting a census for black holes on all scales, mapping radioactive material in young supernova remnants, and exposing relativistic jets of particles from the most extreme active galaxies". This is great news! The hard X-ray sky has not been mapped in any systematic way, and NuSTAR promises to live up to its former unofficial name of Black Hole Finder by discovering the obscured black holes that can not be seen at any other wavelength.

The other primary source of astronomy funding is the National Science Foundation (the NSF), which had been reviewing its priorities under a process called Senior Review that culminated in a report published November 2006. The astronomy division of the NSF has just produced a progress update of how it has been seeking to implement the proposals of the Senior Review. Its worth reading, not least to gain an idea of the problems facing Arecibo's future.

While we're close to home, Bottke et al (2007, Nature, 449, 48) present work suggesting that the KT impactor (i.e. the asteroid impact believed to have lead to the extinction of the non-avian dinosaurs and many other species about 65 million years ago) may have itself originated in the break up of a larger asteroid about 170 million years ago. Those remaining remnants of this mega asteroid (the bits that didn't later hit the Earth or the Moon) make up the Baptistina asteroid family. If you don't have access to Nature then try reading the press release instead.

[Stylish black and white image from the South West Research Institute web site]

Thursday, September 13, 2007

A galactic wind from Messier 100?

Jiménez-Vicente et al (2007) appear to have discovered evidence for a galactic wind emanating from the nuclear region of the roughly face-on spiral galaxy Messier 100
(Astronomy Picture Of the Data image of M100 here). Blue-shifted sodium absorption lines (arising in neutral hydrogen gas at several thousand degrees Kelvin) and blue-shifted hydrogen and nitrogen emission lines (emitted from ionized hydrogen gas at about 10000 Kelvin) are a classic observational signature of a starburst-driven outflow, and their data is pretty persuasive.

These absorption and emission lines arise in gaseous "clouds" that are initially at rest in the host galaxy, but now have been entrained into (and accelerated by the ram pressure of) a much-hotter enveloping wind of merged supernova ejecta (at a temperature of order 10 000 000 Kelvin). In the standard theoretical model for galactic winds the clouds with the lowest column density (i.e. thinnest, lowest mass clouds) are accelerated up to higher velocity than the higher column density clouds, so that the flow ends up multiple clouds covering a broad range of outflow.

It is important to realize that the material seen using optical absorption or emission lines (the clouds) might not necessarily ever achieve the same velocity as the hot, metal-enriched gas that drives the wind, so that the velocity of the clouds is not the same as the true wind outflow velocity.

Constellation-X: There is good news and there is bad news

Last week the National Research Council's Space Studies Board finally published its conclusions assessing the feasibility and priorities for space missions in the NASA "Beyond Einstein" program. Basically this was a match-up to select between current political and fashion favorites going after dark energy, and the older-but-surer science missions like Constellation-X (and X-ray observatory, e.g. for understanding black holes, AGN, and anything else extremely hot in the universe) and LISA (gravitational wave detection).

The committee will be charged to address the following tasks:

1. Assess the five proposed Beyond Einstein missions (Constellation-X, Laser Interferometer Space Antenna, Joint Dark Energy Mission, Inflation Probe, and Black Hole Finder probe) and recommend which of these five should be developed and launched first, using a funding wedge that is expected to begin in FY 2009. The criteria for these assessments include:
a. Potential scientific impact within the context of other existing and planned space-based and ground-based missions; and
b. Realism of preliminary technology and management plans, and cost estimates.

2. Assess the Beyond Einstein missions sufficiently so that they can act as input for any future decisions by NASA or the next Astronomy and Astrophysics Decadal Survey on the ordering of the remaining missions. This second task element will assist NASA in its investment strategy for future technology development within the Beyond Einstein Program prior to the results of the Decadal Survey.

You can read the full report online here. Stein Sigurdsson already offered his take on the predictable outcome (a mission focused on dark energy) in a post last week that can be found here. The Constellation-X team is rather more upbeat in its assessment:

Dear Colleagues:

The BEPAC report provides both bad and good news for the Con-X project. Bad news is that Con-X was not chosen as the highest priority (JDEM was recommended as the first BE mission) or even as the 2nd highest priority (LISA was recommended for enhanced technology investment). Good news can be found in the BEPAC endorsement of the Con-X science and technical readiness. Specifically, "Con-X will make the broadest and most diverse contributions to astronomy of any of the candidate Beyond Einstein missions...the general observer program of Con-X will harness the ingenuity of the entire astronomical community", and "Con-X is one of the best studied and tested of the missions presented to the panel...much of this can be attributed to...strong community support". The panel recognized that "Con-X was ranked second only to the James Webb Space Telescope in the 2001 Decadal Survey".

Looking forward, the BEPAC recommends that "Con-X development activities need to continue aggressively in areas such as achieving the mirror angular resolution, cooling technology and x-ray micro-calorimeter arrays to improve the Con-X missions readiness for the next Astronomy and Astrophysics Decadal Survey." We will continue to pursue technology developments in these areas. All of your assistance in preparing the BEPAC presentations provides us with a very good start for the upcoming Decadal Survey. One of our tasks will be to expand upon the BEPAC material, which was very focused on BE science, in order to capitalize on the breadth and diversity of Con-X science (which was recognized by the BEPAC). We anticipate having the next Con-X FST meeting in mid-Feb 2008, following the release of the NASA budget request for FY2009.

Harvey Tananbaum, Nick White, Michael Garcia, Jay Bookbinder, and Ann Hornschemeier, for the Con-X Project Team.
I leave it as an exercise for the reader to compare the Constellation-X assessment with the officially stated goals of the assessment (1a and b above).

Speaking personally, I'm very disappointed in the selection. Getting the equation of state for dark energy is interesting, but very limited in scope, and this selection basically sacrifices the potential of lot of scientific progress and potential for new discoveries in many branches of astrophysics for a very limited advance in one specific area. Indeed, an area that has little practical impact for our understanding the broader nature of the Universe and how we came to be here (see Simon White's essay regarding dark energy and astronomy here).

Constellation-X is, furthermore, the only proposed instrument in the next 10-20 years with the potential to unambiguously answer the most fundamental unknowns regarding starburst-driven winds (my primary area of study): measuring the velocity of the hot and very hot metal-enriched X-ray-emitting gas. If we don't and won't know that for sure, then we'll never be quite sure about interstellar medium and intergalactic medium feedback processes. Forget about getting the full picture on galaxy formation, galactic chemical evolution, mass loss from galaxies, enrichment and heating of the IGM, and so on. But hey, instead we get to know whether a number called W is between -1 and 1. I'm sure the public is eager to know that, I'm positive they'll get very excited about that result.

Now Con-X isn't officially dead yet, but being third in line is a dangerous place to be. In another few years, if there are further assessments to rationalize and prioritize spending, will Con-X survive? And without Con-X, I feel like I might as well pack up and give in. Game over...

Wednesday, September 05, 2007

Brightest Supernova paper finally published, and its already been demoted to 2nd place

The popular science press and the science blogs went to town back in May 2007 reporting on SN 2006gy, a supernova explosion in the galaxy NGC 1260 that was detected on Earth in 2006. At the time SN 2006gy was heralded as the most luminous SN explosion ever detected.

It is common, but somewhat unfortunate, with "breaking news" about science that the press attention occurs well before the refereed scientific paper describing the results was actually published.

Well, the full, final, refereed paper "SN 2006gy: Discovery of the Most Luminous Supernova Ever Recorded, Powered by the Death of an Extremely Massive Star like η Carinae" by Smith et al was published just this week, in the September 10th edition of the Astrophysical Journal (Smith et al, 2007, ApJ, 666, 1116).

It is somewhat ironic then that in today's astro-ph preprints SN 2006gy is demoted to being the second brightest SN ever by SN 2005ap (Quimby et al, astro-ph/0709.0302). Thats right, a supernovae detected in 2005 was about twice as luminous as 2006gy. Except it'll be published second. But by the same group of researchers.

Both of these events (and a third unusually luminous but as yet unpublished SN event) were detected by the Texas Supernova Search (Quimby, R. 2006a, Ph.D. thesis, Univ. Texas at Austin).

Pretty impressive work, and evidence that unusual things still lurk out there waiting for the innovative scientist (or large team of innovative scientists and engineers) to find them.