Intergalactic 'shot in the dark' shocks astronomers

Dec 18, 2007
Intergalactic 'shot in the dark' shocks astronomers
The robotic Palomar 60-inch telescope imaged the afterglow of GRB 070125 on Jan. 26, 2007. RIGHT: An image taken of the same field on February 16 with the 10-meter Keck I telescope reveals no trace of an afterglow, or a host galaxy. The white cross in this zoom-in view marks the GRB's location. The two nearest galaxies, and their distances, are marked with arrows. Credit: B. Cenko, et al.

A team of astronomers has discovered a cosmic explosion that seems to have come from the middle of nowhere — thousands of light-years from the nearest galaxy-sized collection of stars, gas, and dust. This "shot in the dark" is surprising because the type of explosion, a long-duration gamma-ray burst (GRB), is thought to be powered by the death of a massive star.

"Here we have this very bright burst, yet it's surrounded by darkness on all sides," says Brad Cenko of the California Institute of Technology, Pasadena, Calif., lead author of the team’s paper, which has been accepted for publication in The Astrophysical Journal. "The nearest galaxy is more than 88,000 light-years away, and there's almost no gas lying between the burst and Earth."

The blast was detected on January 25, 2007, by several spacecraft of the Inter-Planetary Network. Observations by NASA's Swift satellite pinpointed the explosion, named GRB 070125 for its detection date, to a region of sky in the constellation Gemini. It was one of the brightest bursts of the year, and the Caltech/Penn State team moved quickly to observe the burst’s location with ground-based telescopes.

Using the team's robotic 60-inch telescope at Palomar Observatory in Calif., the astronomers discovered that the burst had a bright and fast-fading afterglow in visible light. This prompted them to observe the afterglow in detail with two of the world's largest telescopes, the 8-meter Gemini North telescope and 10-meter Keck I telescope, both near the summit of Hawaii's Mauna Kea.

What came next was a total surprise. Contrary to experience with more than a hundred previous GRBs, Gemini spectra revealed no signs of dense gas and dust absorbing the light of the afterglow. A trace of magnesium revealed that the burst took place more than 9.4 billion years ago, as deduced by the shift in wavelength of the afterglow’s light, and that the surrounding gas and dust was more tenuous than the environment around any previous burst.

To further pin down the environment that could produce such an unusual explosion, the group obtained Keck images of the location of GRB 070125 long after its afterglow light had faded away. Surprisingly, the resulting images showed no galaxy at this location. "A Keck image could have revealed a very small, faint galaxy at that distance," says coauthor Derek Fox of Penn State.

Astronomers have amassed a great deal of evidence that GRBs are triggered by the explosive deaths of massive stars, which live very short lives. Because of their short lifespans, massive stars don’t have time to wander far from their birthplaces, usually dense clouds of gas and dust inside respectable-size galaxies. So GRB 070125 raises the perplexing question of how a massive star could be found so far away from any galaxy.

"Big stars live fast and die young, without much time to move around," says Fox. "So if this massive star died far away from any galaxy, the key question is, how did it manage to be born there?" The formation of massive stars requires similarly massive aggregations of gas and dust, which are usually found in bright galaxies.

One possibility is that the star formed in the outskirts of an interacting galaxy, as seen in the famous Hubble Space Telescope picture of the "Tadpole" galaxy, UGC 10214. "In the local universe, about one percent of star formation happens in tidal tails, on the outskirts of two interacting galaxies," says Cenko. "So it might even make sense to find one in 100 gamma-ray bursts in such an environment."

If this idea is correct, it should be possible to detect the tidal tail hosting GRB 070125 by taking a long exposure with the Hubble Space Telescope. "That's definitely our next stop," says Cenko.

"Many Swift discoveries have left astronomers scratching their heads in befuddlement," adds Swift lead scientist Neil Gehrels of NASA Goddard Space Flight Center in Greenbelt, Md. "But this discovery of a long GRB with no host galaxy is one of the most perplexing of all."

Source: Goddard Space Flight Center

Explore further: Astrophysicists offer proof that famous image shows forming planets

Related Stories

NuSTAR captures possible 'screams' from zombie stars

Apr 30, 2015

Peering into the heart of the Milky Way galaxy, NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) has spotted a mysterious glow of high-energy X-rays that, according to scientists, could be the "howls" ...

Giant cosmic tsunami wakes up comatose galaxies

Apr 24, 2015

Galaxies are often found in clusters, with many 'red and dead' neighbours that stopped forming stars in the distant past. Now an international team of astronomers, led by Andra Stroe of Leiden Observatory ...

Recommended for you

Astronomers unveil the farthest galaxy

6 hours ago

An international team of astronomers led by Yale University and the University of California-Santa Cruz have pushed back the cosmic frontier of galaxy exploration to a time when the universe was only 5% of ...

Image: Akari view of the Cygnus region in the Milky Way

May 04, 2015

The constellation of Cygnus is one of the most recognisable in the northern hemisphere. During the summer months, the stars of its long neck stretch along the Milky Way and its wings sweep from side to side.

Image: Hubble eyes galactic refurbishment

May 04, 2015

The smudge of stars at the center of this NASA/ESA Hubble Space Telescope image is a galaxy known as UGC 5797. UGC 5797 is an emission line galaxy, meaning that it is currently undergoing active star formation. ...

Improved detection of radio waves from space

May 04, 2015

Geodesy is the scientific discipline that deals with the measurement of the Earth. One of the measurement techniques it employs uses radio waves from far-distant objects in space to determine factors such ...

User comments : 5

Adjust slider to filter visible comments by rank

Display comments: newest first

MrGrynch
2.5 / 5 (6) Dec 18, 2007
According to plasma cosmology, the universe is pervaded by an intertwined web of Birkeland currents. These currents are normally invisible, and are detectable only by their magnetic tell-tales.

Occasionally, the plasma double layers which separate different charge potentials explode, releasing large amounts of energy. There is no requirement to actually have a star at the location of the explosion in this scenario. The only thing needed is an instability insulating walls of the Birkeland currents. The location of this explosion is likely the nexus of several current strands.
LearmSceince
4 / 5 (6) Dec 18, 2007
According to plasma cosmology,...

Yea.

Or, it could be a hyperspace ship re-entering regular space after suffering an engine-blowout at speed.

Or it could be the "ultimate doomsday weapon" that destroyed the entire galaxy, so naturally we don't see one when looking =after= the event.

mattytheory
2.4 / 5 (5) Dec 18, 2007
I think that it was a binary system that was somehow sling-shotted from its parent galaxy and the GRB we are seeing is the final death-throes of the stars in this binary system merging to form a black-hole.

Any thoughts?
brant
2.6 / 5 (5) Dec 18, 2007
"Astronomers have amassed a great deal of evidence that GRBs are triggered by the explosive deaths of massive stars, which live very short lives."

That is the interpretation. And it does not seem to be true.

We see that their "evidence" does not mean what they thought.
"Polarization in Gamma-Ray Bursts Produced by Pinch Discharge"
http://adsabs.har....5...57W&db_key=AST&data_type=HTML&format=&high=42ca922c9c03905
seanpu
not rated yet Dec 09, 2008

Yea.

Or, it could be a hyperspace ship re-entering regular space after suffering an engine-blowout at speed.

Or it could be the "ultimate doomsday weapon" that destroyed the entire galaxy, so naturally we don't see one when looking =after= the event.


Or maybe a blackhole banished from its host galaxy for insulting the elders found an unsuspecting cloud of gas on which to take its revenge and gobbled it up for dinner one evening whilst pondering how to create its own galaxy to rival his new nemesis.

Get a grip LS, the New Scientific Revolution is coming, no more epicycles, infinite densities, magnetic field ghosts without their charges and star sized billiard-ball physics.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.