The Milky Way is heading for a crash, but it may take 7
billion years.
New Picture: An artist’s rendering provided by the Harvard-Smithsonian Centre
for Astrophysics shows the latest view of the Milky Way’s structure.
According to the most detailed measurements yet,
scientists admitted to have grossly underestimated the mass of the Milky Way,
and so the gravitational pull it exerts on our cosmic neighbours, including the
giant Andromeda galaxy.
The oversight means that the two galaxies, which are on
a cataclysmic collision course, will slam into one another earlier than
scientists had previously predicted.
When the two galaxies meet, powerful shockwaves will
compress interstellar gas clouds within them, triggering a dazzling flourish of
newborn stars, in a last heavenly hurrah before the giant wreckage slowly dims
and dies out.
Fortunately the galactic disaster still lies
unfathomably far into the future.
Our solar system is around 28,000 light years from the
centre of the Milky Way, itself one of more than 35 galaxies in our cosmic
neighbourhood. The Andromeda galaxy, which is twice as wide, is around 2
million light years away.
Karl Menten, an astronomer at the Max Planck Institute
for Radio Astronomy in
A team led by Mr. Menten and Mark Reid at the
Harvard-Smithsonian Centre for Astrophysics in
The scientists recorded intense radio waves coming from
the galaxy’s four spiral arms, where new stars are born. Heat from the stars
warms up molecules of alcohol in interstellar gas clouds, which release the
energy as radio waves.
The new measurements showed that our solar system is
hurtling along at 960,000 kmph, 160,000 kmph faster than thought. “These
measurements are revising our understanding of the structure and motions of our
galaxy,” said Mr. Menten.
The speedier rotation of the galaxy means its mass must
be similar to that of Andromeda, around 270 billion times the mass of the sun,
or 33 per cent greater than earlier calculations have suggested. “No longer
will we think of the Milky Way as the little sister of the Andromeda galaxy,”
said Mr. Reid.
The research was presented at the annual meeting of the
American Astronomical Society in
Astronomers believe the crunch to end all crunches
could happen around the same time our sun is due to burn up the last of its
nuclear fuel, within the next 7 billion years. It is highly unlikely that
planets and stars will collide. Instead the two galaxies will merge to form a
new, large galaxy.
“The galaxies will be dramatically stirred up, but they
are very squidgy, so they will stick together and eventually all the stars will
die out, and it will become one huge, dead galaxy,” said Gerry Gilmore at the
If the galaxy strikes the side of the Milky Way, it is
expected to be pulled back again for further collisions. The whole collision
could take many millions of years.
According to Mr. Gilmore, the research does more than
bring forward the date of our galactic demise. The work also sheds fresh light
on the nature of dark matter, the invisible substance believed to hold galaxies
together. Mr. Gilmore said the findings point to more dark matter at the centre
of the galaxy that may be colder and more compacted than astronomers thought.
Other astronomers at the meeting reported an updated
map of the Milky Way’s spiral arms. It shows two prominent and symmetrical arms
spiralling our of the galaxy’s core, which then branch into four separate arms.
Earlier observations had confused astronomers by revealing different numbers of
spiral arms reaching out from the galaxy’s centre.
— © Guardian Newspapers Limited, 2009
http://www.hindu.com/2009/01/07/stories/2009010755502200.htm