Tuesday, December 18, 2007

The Death Star Galaxy

Being in galaxy in the path of a jet emanating from a supermassive black hole in a neighboring galaxy might be quite catastrophic:

A powerful jet from a super massive black hole is blasting a nearby galaxy, according to new findings from NASA observatories. This never-before witnessed galactic violence may have a profound effect on planets in the jet's path and trigger a burst of star formation in its destructive wake

Known as 3C321, the system contains two galaxies in orbit around each other. Data from NASA's Chandra X-ray Observatory show both galaxies contain super massive black holes at their centers, but the larger galaxy has a jet emanating from the vicinity of its black hole. The smaller galaxy apparently has swung into the path of this jet.

This NASA press release is getting quite a bit of press (e.g. BBC, Yahoo news), and some of the quotes in the press articles certainly spin up the catastrophic angle.

From the BBC article:
The combined effects of this radiation and particles travelling at almost the speed of light could have disastrous consequences for the atmospheres of any Earth-like planets lying in the path of the jet.

For example, protective layers of ozone in the planet's upper atmosphere could be destroyed, which could result in the mass extinction of any life that had evolved on the planet.
From the Yahoo news article:
The larger galaxy has a multi-digit name but is called the "death star galaxy" by one of the researchers who discovered the galactic bullying, Daniel Evans of the Harvard-Smithsonian Center for Astrophysics.

Tens of millions of stars, including those with orbiting planets, are likely in the path of the deadly jet, said study co-author Martin Hardcastle of the University of Hertfordshire in the United Kingdom.

If Earth were in the way — and it's not — the high-energy particles and radiation of the jet would in a matter of months strip away the planet's protective ozone layer and compress the protective magnetosphere, said Evans. That would then allow the sun and the jet itself to bombard the planet with high-energy particles.

And what would that do life on the planet?

"Decompose it," Tyson said.

"Sterilize it," Evans piped in.
However, the actual scientific paper (by Evans et al, still undergoing peer review but available here: astro-ph/0712.2669) wisely ignores the stuff that gets the press excited. None of the speculation regarding zapping planets or star formation in the press stories is in the scientific paper at all. Indeed, its rather sad that the straight facts are not considered exciting enough for the press stories, and instead the speculative stuff gets pushed to the top.

Indeed I have to wonder, given the lack of any discussion in the preprint, if the quotes regarding the effect on planetary atmospheres are based on actual calculations of the estimated particle flux in the target galaxy? Or are they purely speculation based a the hard-to-resist gut feeling that "blacks holes are powerful, so they must be capable of anything"?

Speaking in general (as I don't know the answer to the questions above) I feel this is a real problem with press releases and articles that deviate from the actual scientific paper - the public is potentially being fed speculation rather than the actual peer-reviewed science.

Now it is possible that the quotes in the press articles are based on quantitative comparisons to other peer-reviewed literature on the effect astrophysical events may have on planetary atmospheres or biological activity - the trouble is we don't and can't easily know whether this is the case.

There have been calculations of the effect of nearby supernovae, Gamma Ray bursts on the atmosphere of Earth-like planets (e.g. Smith et al, 2004, Icarus, 171, 229; Scalo & Wheeler, 2002, ApJ, 566, 723; Hunt, 1978, Nature, 271, 430), and also of the effects of neutron star mergers (Dar et al, 1998, Phys Rev Letters, 80, 5813), but I am not aware of equivalent publications regarding jets from AGN.

The image shown comes from the press release, and is described in the accompanying caption:

This composite image shows the jet from a black hole at the center of a galaxy striking the edge of another galaxy, the first time such an interaction has been found. In the image, data from several wavelengths have been combined. X-rays from Chandra (colored purple), optical and ultraviolet (UV) data from Hubble (red and orange), and radio emission from the Very Large Array (VLA) and MERLIN (blue) show how the jet from the main galaxy on the lower left is striking its companion galaxy to the upper right. The jet impacts the companion galaxy at its edge and is then disrupted and deflected, much like how a stream of water from a hose will splay out after hitting a wall at an angle.

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