Friday, September 28, 2012

A Busy Week in Astronomy

SN 2009ip Finally Becomes a Supernova

This week was full of interesting astronomy stories that received a lot of press coverage. I'll give a run-down of them in a moment, but I'll begin with a story that received little fanfare because it has moved too quickly for publicity. Last night a very interesting paper appeared on the arXiv: "The Unprecedented Third Outburst of SN 2009ip: A Luminous Blue Variable Becomes a Supernova" by Jon Mauerhan et al. This is about an object that was classified as a supernova back in 2009 but turned out not to be a supernova, after further study. The rapid brightening seen in 2009 was actually a violent outburst and a similar event was seen in 2010. A third outburst has now been observed, and this time a true core-collapse supernova appears to have occurred, as reported in the new paper. The progenitor star was a "luminous blue variable" (LBV), a massive star that is extremely bright, hot and erratic. Now, it appears to be gone. This is an exciting result, since it would be the first time that a massive, blue star, with well-observed LBV outbursts, has been caught turning into a core-collapse supernova.

The science is fascinating, but there's a remarkable aspect to how this work was done. The new spectra were obtained on September 16, 17, and 27 at Kitt Peak and on September 23 at Keck, and the new photometry was obtained on dates ranging from August 28 to September 26 at Lick, and on September 24 at Mt. Bigelow. All of those dates are for 2012. The paper was submitted on 2012 September 27. So, the paper was submitted on the same day as some of the data was obtained.  That is some super-fast data reduction, figure preparation and paper writing. I have no idea how you do that, and I don't care how much team work is involved and how little sleep you can tolerate. Also, before you question the caliber of the authors, it's not like these are charlatans mocking the ability to freely post to the arXiv. Having done some publicity work with the 2nd and 3rd authors, Nathan Smith and Alex Filippenko, I know about their high standards.

The case for it being a supernova wasn't always clear during the week. I followed the results as they came in thanks to Astronomer's Telegrams tweeted by Bob Rutledge, from McGill University. Bob is also the Editor-in-Chief of The Astronomer's Telegram. The first ATel I saw was "SN 2009ip: an LBV becomes a real supernova" but then follow-up observations by Swift and ground-based observatories suggested that a true supernova hadn't occurred because it didn't get brighter. Could astronomer's have been wrong again about SN 2009ip? I tweeted that rumors of the star's demise had been exaggerated. But then further, substantial brightening was noted by an observer from Coral Towers Observatory and a team from Harvard, strengthening the case for a supernova. At that stage Bob Rutledge told me he thought it was either a supernova or a "never-before-seen headfake by an LBV." New spectra from Nathan Smith and Jon Mauerhan and a team from UCSD then confirmed it as provided extra evidence it was a supernova.

Mauerhan et al. presumably submitted their paper very quickly so they would beat all of the different teams working on this object. Work on transient phenomena, like supernovas and gamma-ray bursts, tends to be a very competitive area. It wouldn't be surprising if several other papers appear in the next few weeks.

Returning to the science: the star that appears to have exploded was estimated to have had a mass between 50 and 80 times that of the sun, which is a whole lot of star. As Mauerhan et al point out, some models predict that very massive stars will end their lives as "failed" supernovas, where the star collapses to form a black hole without producing a spectacular light show. Based on the brightness of this event this wasn't a failed supernova, but this doesn't mean a black hole did not form. Many questions remain about the details of the explosion and the outbursts seen in 2009 and 2010.

A Cosmic Week

The week started with a Chandra X-ray observatory press release issued by us at the Chandra X-ray Center, on the detection of an enormous halo of gas around the Milky Way. A number of articles were written about the result including these by Jason Major, Matthew Francis, and Alex Knapp.

An artist's impression of the halo of gas around the Milky Way. Credit: NASA/CXC/M.Weiss; NASA/CXC/Ohio State/A Gupta et al
On Tuesday, the deepest image ever obtained was released. Articles on the eXtreme Deep Field, taken by the Hubble Space Telescope, include these by Nancy Atkinson and Clara Moskowitz.

The Hubble eXtreme Deep Field. Credit: NASAESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team
A day later, a new result came out in Nature about the origin of a bright supernova, SN 1006, in our galaxy. For more details, please see these articles by Kelly Oakes and Charles Choi. A beautiful composite image of the remains of this supernova appeared on the cover of Nature and was produced by us here at the Chandra X-ray Center. It includes Chandra, VLA and Hubble data.

SN 1006. Credit: X-ray: NASA/CXC/Rutgers/G.Cassam-Chenaï, J.Hughes et al.; Radio: NRAO/AUI/NSF/GBT/VLA/Dyer, Maddalena & Cornwell; Optical: Middlebury College/F.Winkler, NOAO/AURA/NSF/CTIO Schmidt & DSS
Yesterday there were two big astronomy stories. First, astronomers were able to study material very close to the event horizon of the supermassive black hole in M87. For details about the result and its implications, see these articles by Matthew FrancisJohn Matson, John Timmer, Charles Choi, and Clara Moskowitz.

Finally, the Mars Curiosity Rover has found evidence that a stream once ran across the area where it is  driving. Alicia Chang's article has appeared in many places, including the Huffington Post and numerous other articles have appeared, including these by Elizabeth Landau, Lisa GrossmanMarc Kaufman, and Amina Khan. It's clear that the Curiosity Rover has been an outstanding success and I look forward to more discoveries.

1 comment:

  1. A nice summary of the week's announcements, Peter.

    I think the 'eXtreme Deep Field' image will prove to be the most significant of them, probing deeper into space than ever before, in the visible and near infrared wavelengths. We must keep Hubble going!