Gamma Rays and Civilizations

by Paul Gilster on December 18, 2007

Lately I’ve been thinking about cosmic killers, the kind of extinction events that could destroy an entire ecosphere and any civilization living within it. It’s a natural enough thought given our speculations about life elsewhere in the universe. Just how hostile a place is the Milky Way? We’re beginning to learn that planets are abundant around stars in our region of the disk, with the encouraging expectation that habitats for evolving lifeforms must be widespread. But maybe there are natural caps other than technological suicide that could end a civilization’s dreams.

You can’t help pondering this when you run into the recent news about a long duration gamma-ray burst (GRB) that took astronomers by surprise. GRBs are normally thought to flag the death of a massive star, but in this case the burst seems to come out of nowhere. What caused the event in a region of space where the nearest galaxy is 88,000 light years away? And no question about GRB 070125′s credentials. It was detected and corroborated last January and its location readily pinpointed in Gemini.

A long galactic tail

So did a massive star find its way out into the depths of intergalactic space? If so, it was an unusual one, for the kind of stars we’re talking about lead short lives and by necessity remain close to the clouds of gas and dust inside galaxies that gave them birth. Research now turns to the question of whether the star in question could have formed in the ‘tidal tail’ between two interacting galaxies. Such tails can be extraordinarily faint. Hubble may be able to tell us whether or not this is true, in which case the burst will have shown us a star-forming region we didn’t know was there.

Image: A recent galaxy collision produced the long tail in the Tadpole Galaxy. If GRB 070125 exploded in a similar tail, only Hubble could detect the tail. Credit: NASA, H. Ford, et al.

Of course, where gamma-ray bursts are concerned, the farther away, the better. But there are other interesting sources of trouble besides GRBs. Consider 3C321. The two galaxies orbiting each other that make up this celestial object made enough of a splash that my local newspaper picked up the story, an unusual addition for a normally astronomy-free venue. Both these galaxies, according to Chandra X-ray Observatory data, contain supermassive black holes, but the larger galaxy shows a jet that seems to be pointed right at the smaller. That could make things interesting indeed at the receiving end, as Dan Evans (Harvard-Smithsonian Center for Astrophysics) is quick to point out:

“We’ve seen many jets produced by black holes, but this is the first time we’ve seen one punch into another galaxy like we’re seeing here. This jet could be causing all sorts of problems for the smaller galaxy it is pummeling.”

Indeed. High-energy X-rays and gamma rays aren’t conducive to long lifetimes, with potentially lethal effects for the atmospheres of planets that happen to be in the way. The two galaxies are separated by a scant 20,000 light years, so the effect is about the same as if a jet from the Milky Way’s core illuminated our position in the Orion Arm. Which brings to mind disaster scenarios like that found in Richard Cowper’s wonderful Twilight of Briareus, where a future Earth is transformed by a supernova (not GRB) explosion, with results that awaken in humans a strange, latent potential (regulars here know of my admiration for Cowper).

That’s quite a benign result compared to what might happen with a full-bore hit from a nearby GRB or a major jet. Fortunately for life’s chances, alignments like that seen in 3C321 seem vanishingly rare. As for that unusual GRB in Gemini, the evidence says GRB 070125 took place some 9.4 billion years ago. We know all too little else. “Many Swift discoveries have left astronomers scratching their heads in befuddlement,” says Swift lead scientist Neil Gehrels (NASA GSFC). “But this discovery of a long GRB with no host galaxy is one of the most perplexing of all.”

More surprises are likely. Last December Nature reported on GRBs in a series of papers, focusing particularly on the interesting GRB 060614. This was an extremely long (102 seconds) burst from 1.6 billion light years away in the constellation Indus. No trace of a supernova could be found that would explain it. Another burst, GRB 060505, likewise left no supernova remnant. All of which leaves this observer thinking GRBs have much to teach us, particularly in terms of understanding the celestial events that give them birth. As for extinction events, GRBs do, at least, seem to be tightly beamed, good news for all but the unlucky.

{ 11 comments }

ljk December 18, 2007 at 15:32

A Radio Through X-ray Study of the Jet/Companion-Galaxy Interaction in 3C 321

Authors: Daniel A. Evans (1,2), Wen-Fai Fong (1,3), Martin J. Hardcastle (4), Ralph P. Kraft (2), Julia C. Lee (1,2), Diana M. Worrall (5), Mark Birkinshaw (5), Judith H. Croston (4), Tom W. B. Muxlow (6) ((1) Harvard University, Department of Astronomy, (2) Harvard-Smithsonian Center for Astrophysics, (3) Massachusetts Institute of Technology, (4) University of Hertfordshire, (5) University of Bristol, (6) MERLIN/VLBI National Facility, Jodrell Bank Observatory)

(Submitted on 17 Dec 2007)

Abstract: We present a multiwavelength study of the nucleus, environment, jets, and hotspots of the nearby FRII radio galaxy 3C 321, using new and archival data from MERLIN, the VLA, Spitzer, HST, and Chandra. An initially collimated radio jet extends northwest from the nucleus of its host galaxy and produces a compact knot of radio emission adjacent (in projection) to a companion galaxy, after which it dramatically flares and bends, extending out in a diffuse structure 35 kpc northwest of the nucleus.

We argue that the simplest explanation for the unusual morphology of the jet is that it is undergoing an interaction with the companion galaxy. Given that the northwest hotspot that lies greater than 250 kpc from the core shows X-ray emission, which likely indicates in situ high-energy particle acceleration, we argue that the jet-companion interaction is not a steady-state situation. Instead, we suggest that the jet has been disrupted on a timescale less than the light travel time to the end of the lobe, $\sim 10^6$ years, and that the jet flow to this hotspot will only be disrupted for as long as the jet-companion interaction takes place.

The host galaxy of 3C 321 and the companion galaxy are in the process of merging, and each hosts a luminous AGN. As this is an unusual situation, we investigate the hypothesis that the interacting jet has driven material on to the companion galaxy, triggering its AGN. Finally, we present detailed radio and X-ray observations of both hotspots, which show that there are multiple emission sites, with spatial offsets between the radio and X-ray emission.

Comments: 13 pages, 9 figures. A high-resolution version is available from this http URL

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0712.2669v1 [astro-ph]

Submission history

From: Daniel Evans [view email]

[v1] Mon, 17 Dec 2007 20:34:34 GMT (418kb)

http://arxiv.org/abs/0712.2669

Iron Sun December 19, 2007 at 0:14

If you want an excellent description of the effect a nearby GRB would have onthe Earth, read Diaspora by Greg Egan. It’s a fantastic hard-science book.

Administrator December 19, 2007 at 11:10

Thanks for the tip re Greg Egan’s book, a title I’m not familiar with. Diaspora goes immediately to the top of my reading list.

ljk December 21, 2007 at 10:28

LIGO SHEDS LIGHT ON COSMIC EVENT (ASTRONOMY)

An analysis by the international LIGO (Laser Interferometer
Gravitational-Wave Observatory) Scientific Collaboration has
excluded one previously leading explanation for the origin of an
intense gamma-ray burst that occurred last winter. Gamma-ray bursts
are among the most violent and energetic events in the universe, and
scientists have only recently begun to understand their origins.

Details: http://mr.caltech.edu/media/Press_Releases/PR13084.html

James M. Essig December 23, 2007 at 17:11

Hi Folks;

Gamma ray bursts are indeed a fascinating phenomenon. The lie at the extreme end of our known physics to describe and may even require some new physics to explain, at the very least new applied physics concepts. It is kind of humbling to think that our civilization could end as a result of a nearby gamma ray burst. It is staggering to contemplate the cause of the most energetic gamma ray events ever recorded. There is some cool physics at work here. As our scientific instruments become more sensitive and as they involve ever new forms of observational energy such as the LIGO facilities and the neutrino telescopes/detectors burried underneath the Antarctic Ice, many cool things await us. Some of this gained knowledge will no doubt at least indirectly support manned interstellar travel.

To all of humanity, I would like to wish a very Happy Holiday as we ponder what dreams may come in the new year, the next decade, and the next century as we venture out among the stars as an interstellar space faring civilization.

Thanks;

Jim

ramkumar December 24, 2007 at 7:00

As the topic puts it What will be the effect of Gamma ray burts on
Civilization in other planets . Perhaps annihilation of the entire race in a planet is a common phenimina if u look in the cosmic scale , Other thing being distintegration of Galastic center & a star getting burned out of Fuel .

James M. Essig December 24, 2007 at 14:03

Hi ramkumar;

I saw a television ducumentary suggesting that if a gamma ray burst came from the supernova of the unstable star, Eta Carinae, which lies about 7500 light-years from Earth, the entire mammalian population and all normal plant life on the side of the planet facing the gamma ray burst might be killed by the huge gamma ray flux followed by a breakdown of the ecosytem supporting other life forms as a result of the near complete or total destruction of the Ozone Layer and other destructive atmospheric chemisty effects.

I can imagine there have been many many ETI civilizations that have been wiped out by gamma ray bursts and supernova within the history of the observable universe, even ETI civilizations much more advanced than ours. In a sense, the cosmos is like a long term shooting gallery.

Thanks;

Jim

ljk January 9, 2008 at 9:34

NASA AND GEMINI PROBE MYSTERIOUS EXPLOSION IN THE DISTANT PAST

GREENBELT, Md. – Using the powerful one-two combo of NASA’s Swift satellite and the Gemini Observatory, astronomers have detected a mysterious type of cosmic explosion farther back in time than ever before. The explosion, known as a short gamma-ray burst (GRB), took place 7.4 billion years ago, more than halfway back to the Big Bang.

“This discovery dramatically moves back the time at which we know short GRBs were exploding. The short burst is almost twice as far as the previous confirmed record holder,” says John Graham of the Johns Hopkins University, in Baltimore, Md. Graham is presenting his group’s discovery on Tuesday in a poster at the American Astronomical Society’s 2008 winter meeting in Austin, Texas.

GRBs are among the most powerful explosions in the universe, releasing enormous amounts of energy in the form of X-rays and gamma rays. Most bursts fall in one of two categories: long bursts and short bursts, depending on whether they last longer or shorter than three seconds. Astronomers think that long GRBs are triggered by the collapse and explosion of massive stars. In contrast, a variety of mechanisms have been proposed for short bursts. The most popular model says that most short GRBs occur when two neutron stars smash into each other and collapse into a black hole, ejecting energy in two counterflowing beams.

The record-setting short burst is known as GRB 070714B, since it was the second GRB detected on July 14, 2007. Swift discovered the GRB in the constellation Taurus. The burst’s high energy and 3-second duration firmly place it in the short GRB category. Rapid follow-up observations with the 2-meter Liverpool Telescope and the 4-meter William Herschel Telescope found an optical afterglow in the same location as the burst, which allowed astronomers to identify the GRB’s host galaxy.

Next, Graham and his colleagues, Andrew Fruchter of the Space Telescope Science Institute, in Baltimore, and Andrew Levan of the University of Warwick, U.K., trained the 8-meter Gemini North Telescope in Hawaii on the galaxy. It revealed that the host galaxy has a spectral line from ionized oxygen. The amount that line was shifted toward the red end of the spectrum yields a redshift of 0.92. A redshift of 0.92 translates to a distance of 7.4 billion light-years, meaning the explosion occurred 7.4 billion years ago.

“The fact that this short burst is so far away means this subclass has a broad range of distances, although they still tend to be closer on average than long GRBs,” says Swift lead scientist Neil Gehrels of NASA’s Goddard Space Flight Center in Greenbelt, Md.

Gehrels adds that GRB 070714B’s energy is about 100 times higher than average for short bursts, and is more similar to the typical energy of a long GRB. “It is unclear whether another mechanism is needed to explain this explosion, such as a neutron star-black hole merger. Or it could be that there are a wide range of energies for neutron star-neutron star mergers, but that seems unlikely.”

Another possibility is that GRB 070714B concentrated its energy in two very narrow beams, and one of the beams happened to be aimed directly at Earth. This would make the burst seem more powerful than it really was. Perhaps most short GRBs eject their energy in wider and less-concentrated beams.

“We now have a good idea of the type of star that produces the brighter long bursts. But how short bursts are formed remains a mystery,” says Fruchter.

Swift is managed by NASA Goddard and was built and is operated in collaboration with Penn State University, the Los Alamos National Laboratory, and General Dynamics in the U.S.; the University of Leicester and Mullard Space Sciences Laboratory in the U.K.; Brera Observatory and the Italian Space Agency in Italy; plus partners in Germany and Japan.

For related images to this story, please visit on the Web:

http://www.nasa.gov/centers/goddard/news/topstory/2007/gemini_explosion.html

ljk March 3, 2008 at 10:17

Deathstar a risk to Earth: astronomer

March 3, 2008 – 5:25PM

Earth may be staring down the barrel of one of the galaxy’s
most beautiful and potentially deadly objects.

A highly unstable star at the end of its life could unleash a
burst of gamma-ray radiation directed straight at Earth, any
time between now and the next couple of hundred thousand
years.

University of Sydney astronomer Peter Tuthill discovered
an elegant rotating pinwheel system known as WR104 in the
constellation Sagittarius eight years ago.

It contains a Wolf-Rayet star, the last stop in a star’s life
before it explodes in a massive supernova.

While studying WR104′s striking and colourful shape, Dr Tuthill
noticed that the perfect spiral he was observing could only
occur when staring right down the centre of it.

Full article here:

http://news.theage.com.au/deathstar-a-risk-to-earth-astronomer/20080303-1wj7.html

ljk June 27, 2008 at 11:30

ESLAB 42: COSMIC CATACLYSMS AND LIFE

10-14 November 2008

3rd announcement

The 42nd ESLAB symposium will be held from 10 -14 November
2008 at Frascati, Italy. The theme of this symposium is “Cosmic
Cataclysms and Life”.

A number of cataclysms have occurred in the history of the
universe and the Solar System. This Symposium reviews those
that had a critical influence on the evolution of habitable worlds
and on the emergence and survival of life on Earth, and
possibly elsewhere.

The Call for Abstracts has been issued with a submission
deadline of 17 July. Further details on the programme and the
list of invited speakers are available at:

http://sci.esa.int/jump.cfm?oid=42996

ljk July 7, 2008 at 11:58

“Classifying Extinction Risks” by Michael Anissimov at:

http://lifeboat.com/ex/classifying.extinction.risks

EVENTS

The Global Catastrophic Risks Conference will be held July 17
to July 20 at the University of Oxford. Our James Hughes,
Anders Sandberg, Mike Treder, and Eliezer Yudkowsky will
be speaking. Learn more at:

http://global-catastrophic-risks.com/aboutconf.html

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