NASA’s Chandra X-ray Observatory has discovered rich deposits of neon,
magnesium, and silicon in a pair of colliding galaxies known as The
Antennae. When the clouds in which these elements are present cool, an
exceptionally high number of stars with planets should form. These results
may foreshadow the fate of the Milky Way and its future collision with the
Andromeda Galaxy.

“The amount of enrichment of elements in The Antennae is phenomenal,” said
Giuseppina Fabbiano of the Harvard-Smithsonian Center for Astrophysics (CfA)
in Cambridge, Mass. at a press conference at a meeting of the American
Astronomical Society in Atlanta, Ga. “This must be due to a very high rate
of supernova explosions in these colliding galaxies.” Fabbiano is lead
author of a paper on this discovery by a team of U.S. and U.K. scientists
that will appear in an upcoming issue of The Astrophysical Journal Letters.

When galaxies collide, direct hits between stars are extremely rare, but
collisions between huge gas clouds in the galaxies can trigger a stellar
baby boom. The most massive of these stars race through their evolution in a
few million years and explode as supernovas. Heavy elements manufactured
inside these stars are blown away by the explosions and enrich the
surrounding gas for thousands of light years.

“The amount of heavy elements supports earlier studies that indicate there
was a very high rate of relatively recent supernovas, 30 times that of the
Milky Way,” according to collaborator Andreas Zezas of the CfA.

The supernova violence also heats the gas to millions of degrees Celsius.
This makes much of the matter in the clouds invisible to optical telescopes,
but it can be observed by an X-ray telescope. Chandra data revealed for the
first time regions of varying enrichment in the galaxies – in one cloud
magnesium and silicon are 16 and 24 times as abundant as in the Sun.

“These are the kinds of elements that form the ultimate building blocks for
habitable planets,” said Andrew King of the University of Leicester, U.K.
and a coauthor of the study. “This process occurs in all galaxies, but it is
greatly enhanced by the collision. Usually we only see the new elements in
diluted form as they are mixed up with the rest of the interstellar gas.”

CfA coauthor Alessandro Baldi commented that, “This is spectacular
confirmation of the idea that the basis of chemistry, of planets, and
ultimately of life is assembled inside stars and spread through galaxies by
supernova explosions,”

As the enriched gas cools, a new generation of stars will form, and with
them new planets. A number of studies indicate that clouds enriched in
heavy elements are more likely to form stars with planetary systems, so in
the future an unusually high number of planets may form in The Antennae.

“If life arises on a significant fraction of these planets, then in the
future the Antennae will be teeming with life,” speculated Francois
Schweizer, another coauthor who is from the Carnegie Observatories in
Pasadena, Calif. “A vast number of Sun like stars and planetary systems
will age in unison for billions of years.”

At a distance of about 60 million light years, The Antennae system is the
nearest example of a collision between two large galaxies. The collision,
which began a couple of hundred million years ago, has been so violent that
gas and stars from the galaxies have been ejected into the two long arcs
that give the system its name. The Chandra image shows spectacular loops of
3-million-degree gas spreading out south of the antennae. “These loops may
be carrying out some of the elements dispersed by supernovas into
intergalactic space,” said Trevor Ponman of Birmingham University, U.K.

The Antennae give a closeup view of the type of collisions that were common
in the early universe and likely led to the formation of most of the stars
that exist in the universe today. They may also provide a glimpse of the
future of our Milky Way Galaxy, which is on a collision course with the
Andromeda Galaxy. At the present rate, a crash such as the one now occurring
in the Antennae could happen in about 3 billion years. Tremendous
gravitational forces will disrupt both galaxies and reform them, probably as
a giant elliptical galaxy with hundreds of millions of young Sun like stars,
and possibly planetary systems.

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra
program for the Office of Space Science, NASA Headquarters, Washington.
Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime
development contractor for the observatory. The Smithsonian Astrophysical
Observatory controls science and flight
operations from the Chandra X-ray Center in Cambridge, Mass.

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