The Earth is under constant barrage by radio signals
from space. Typically they just come from mundane sources like our own
satellites, your 'garden variety' stars, and even more exotic things
like 'rotating neutron stars'. However, astronomers have found one type of signal whose source has, so far, remained a mystery.
No, I'm not talking about the 'Wow! signal' (although that's a great one).
For us, this story starts in 2007, when a team of astronomers reported
finding an incredibly powerful and incredibly short radio burst, from a
sky survey done back in 2001. It had flashed very 'bright' to their
radio telescope for about 5 milliseconds and then it was gone. The pulse
itself wasn't the first thing that struck them as odd, though; it was
that the pulse didn't repeat. Looking at it a bit closer, they found
that it got even stranger, because it came from a point in the sky that
suggested it originated from outside our galaxy. In fact, they found
that whatever sent forth this blast of radio waves was roughly 3 billion light years away, so not even in our galactic neighbourhood (for comparison, the Andromeda Galaxy is 'only' 2.5 million light years away).
[ Related: Pluto’s newest moons now called Kerberos and Styx ]
This mysterious radio signal became known as the 'Lorimer burst', named after National Radio Astronomy Observatory astrophysicist Duncan Lorimer, who led the team that discovered and studied the burst.
Now, fast-forward to today, and astronomers have published another study
that examines four more of these signals they detected over the last
four years. That's not the only ones they've seen, though. According to ABC Science,
the astronomers set up a permanent detector that sees one of these
bursts every 10 days or so. Their research only covers four of them
because the radio telescope can only cover a very small area of the sky
at any time.
These bursts are all from single events (as opposed to the same
object emitting repeated bursts), that happened billions of light years
away (so billions of years ago), but their source is still a mystery.
They're definitely caused by some kind of cataclysmic astronomical event — maybe a massive supernova that forms a black hole or two neutron stars colliding, but the leading contender is something that may be even more strange — a magnetic neutron star, or 'magnetar'.
A neutron star
is what's left over when a star that's many times bigger than our Sun
dies. This stellar 'remnant' is typically about 20 kilometres in
diameter, and so dense that a mere thimble-full of its matter would
weigh over 100 million tons. Some neutron stars rotate very quickly (on
the order of milliseconds per rotation) and put off beams of radiation
from their poles, a bit like a lighthouse shining a beacon across space.
These are called 'pulsars'.
A magnetar is a neutron star that rotates much slower ('only' once
every few seconds) and has incredibly powerful magnetic fields. For
comparison, the strength of our own Sun's magnetic field is measured in micro-Teslas — millionths of a unit of magnetic field strength. A magnetar's magnetic field strength is measured in hundreds of millions to hundreds of billions of Telsas.
"These are the most magnetic stars in the universe, and every now and
then they have very large explosions on them, which may be a good
candidate for the origin of these things," said Prof. Matthew Bailes,
the director of the Swinburne Centre for Astrophysics and Supercomputing, in Melbourne, Australia, according to ABC Science.
"They can give off as much energy as the Sun does for 300,000 years, in just a millisecond."
It's this potential for such incredibly powerful bursts of energy
that puts them at the top of the list of suspects. Anything weaker and
the signal wouldn't survive crossing intergalactic space to reach us.
Another exceptional thing about these bursts is that they carry information along with them about the universe.
"Every time the radio waves go past an electron, the electron's presence gets encoded in the burst of photons," Bailes told ABC Science.
"We can use this to count how many electrons there are between us and
half way across the universe, which is incredibly exciting because
almost all of the normal atoms are actually not in galaxies, they're
just sitting around in the intergalactic medium."
[ More Geekquinox: DNA study ties B.C. First Nations groups to ancient ancestors ]
Astronomers have used the beams of pulsars to tell us about what lies
between the pulsar and us, but in this case, it may be one mystery
helping us to solve another mystery. We may not know where these bursts
are coming from, but the bursts themselves will be able to tell us a lot
about the universe we live in.
"We are still not sure about what makes up the space between
galaxies, so we will be able to use these radio bursts like probes in
order to understand more about some of the missing matter in the
Universe," said study co-author Dr. Ben Stappers, from Manchester’s School of Physics and Astronomy, according to a news release.
"We are now starting to use Parkes and other telescopes, like the
Lovell Telescope of the University of Manchester, to look for these
bursts in real time."
No comments:
Post a Comment