Object type: Galaxy
Distance: 300 million light-years
Distance: 300 million light-years
A wounded galaxy is bleeding an astonishingly long trail of gas into space, yet there is no obvious perpetrator.
Frustrating even the most resolute of
cosmic detectives, this crime scene illustrates the dangers that
galaxies face – the loss of such a large volume of gas can eventually
kill. It also suggests we may need to revise our theories of how and
where they can be wounded.
Space is a dangerous place for
galaxies. Collisions with other galaxies, near misses and other forms of
violence can dramatically alter or even destroy them.
Our own Milky Way has gobbled up smaller galaxies in the past and is expected to be transformed from an elegant spiral into a diffuse blob of stars in a likely merger with the nearby Andromeda galaxy
a few billion years from now.
a few billion years from now.Hydrogen trail
Even when disturbances do not destroy galaxies, they can strip them of the gas they need to produce new generations of stars and planets, effectively sterilising them.
The latest known victim of such
intergalactic violence is called FGC 1287. It appears perfectly healthy
in visible light, which shows only its stars, but new radio evidence
from the Very Large Array in New Mexico reveal that it is severely
wounded, bleeding a vast trail of gas into space.
This galactic tail is one of the
longest ever seen, stretching across 800,000 light years. "When we
looked at the data, we were amazed," says Tom Scott of the Andalucia Institute of Astrophysics in Granada, Spain, who led the study.
The tail is made of billions of suns'
worth of hydrogen gas that has somehow bled from FGC 1287 – more gas
than remains in the galaxy itself. But the cause of the galactic
haemorrhage is hard to pin down.
Bloody footprints
"FGC 1287 is completely different from any case we have seen before," says team member Luca Cortese of the European Southern Observatory in Garching, Germany.
One possible explanation is the
galaxy's location at the edge of a cluster of other galaxies. When a
galaxy falls into a cluster, it often has gas stripped away by
"headwinds" created as the galaxy moves through the cluster's own gas.
But X-ray observations of the
cluster's gas suggest it is too thin at FGC 1287's location to make the
galaxy feel much of a wind, says the team.
A near miss with another galaxy might
be a better lead and could explain why the galaxy's stars are not in
disarray. In a brief encounter at high speed, the second galaxy's
gravity could have pulled away loosely bound gas without disturbing its
stars, which are more tightly bound to the galaxy by gravity.
Intriguingly, like bloody footprints leaving a crime scene, the gas
trail points in the direction of another galaxy.
Violent mystery
The case is not closed, however,
because the suspect galaxy looks much less massive and shows no sign of
trauma itself. It is not clear how it could have made such a large
impact on the heavier galaxy without being wounded itself.
That leaves FGC 1287's condition a
mystery. Whatever the solution, the team say the case suggests we have a
lot to learn about how violence befalls galaxies. Perhaps FGC 1287 is
enduring stronger winds than expected, or another galaxy not obviously
connected to it will turn out to be its attacker.
"This discovery might open a new chapter in our understanding of environmental effects on galaxy evolution," says team member Elias Brinks of the University of Hertfordshire, UK.
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