Space Fan News #54: Galaxy's Black Hole Belches; Venus is Slowing Down; Baffling Brown Dwarf


Uploaded by tdarnell on 10.02.2012

Transcript:
Hello Space Fans and welcome to another edition of Space Fan News.
Coincidentally, last week, I released a video about the black hole at the center of our
galaxy and the large gas cloud that is heading for it and should start interacting with it
sometime in the next few years or so.
What I didn't mention in that video was that our black hole has a name, Sagittarius A*,
and it turns out that it has quite an appetite, and it belches.
This week, astronomers released some research which shows that our little black hole is
grazing on asteroids and comets and other debris from the galaxy. How do they know this?
Well for many years now, the Chandra X-ray space telescope has detected X-ray flares
about once a day from Sagittarius A*, I'm going to call it "Sag A*" from now on. See?
Belches. X-ray belches.
The flares last a few hours with brightness ranging anywhere from a few times to nearly
one hundred times that of the black hole's regular output. They have also been seen in
infrared data from ESO's Very Large Telescope in Chile.
So this team is suggesting that there is a cloud around Sag A* containing hundreds of
trillions of asteroids and comets, which were stripped from their parent stars and eventually
made their way towards the center of the galaxy and around the black hole. As the asteroids
fall in and pass within about 100 million miles of the black hole, which is roughly
the distance between the Earth and the sun, they are torn into pieces by gravitational
tidal forces.
These pieces then become vaporized by friction as they pass through the hot, thin gas flowing
onto Sgr A*, this is similar to what happens when a meteor falls to earth, it heats up
and glows as it falls through the atmosphere. As the asteroid or comet falls in, a flare
is produced and the remains of the asteroid are eventually swallowed by the black hole.
The astronomers estimate that it would take asteroids larger than about six miles in radius
to generate the flares observed by Chandra. Now, Sag A* may also be consuming smaller
asteroids, but these would be hard to spot because the flares they generate would be
much fainter.
One really cool thing these guys did was they worked out over the 10 billion year lifetime
of our galaxy, only a few trillion asteroids should have been removed by the black hole.
This means that only a small fraction of the total would have been consumed, so the supply
of asteroids would hardly be depleted.
So it sounds like there's plenty of food on the table for Sag A*.
Next, ESA’s Venus Express spacecraft - in orbit around, that's right, you guessed it,
Venus, has discovered that Venus is spinning a little slower than previous measurements.
Peering through the dense atmosphere in the infrared, the orbiter found surface features
were not quite where they should be.
Using the VIRTIS instrument at infrared wavelengths to penetrate the thick cloud cover, scientists
studied Venus' surface features and discovered that some were displaced by up to 20 km from
where they should have been given the accepted rotation rate which was measured by NASA’s
Magellan orbiter in the early 1990s.
The reason the orbiter is there in the first place is they are trying to find out whether
Venus has a solid or a liquid core, and these detailed measurements are designed to help
them find that out.
If it has a solid core, that means its mass must be more concentrated towards the center.
If that's the case, then the planet’s rotation would react less to external forces.
The most important thing in all of this is the dense atmosphere – it has more than
90 times the pressure of Earth’s and it also has high-speed weather systems, with
clouds running and wind blowing all over the place, which are believed to change the planet’s
rotation rate through friction with the surface.
Here on Earth we see a similar effect, where it is largely caused by wind and tides. The
length of an Earth day can change by roughly a millisecond and changes seasonally with
wind patterns and temperatures over the course of a year.
So we see it here too, it's just such a tiny effect that it doesn't really matter.
Back in the 1980s and 1990s, the Venera and Magellan orbiters made radar maps of the surface
of Venus. Prior to that, we had never see the surface before because of the dense, crushing
and poisonous atmosphere. These maps gave us our first detailed global view of this
hostile world.
Over its four-year mission, Magellan was able to watch features rotate under the spacecraft
and it measured their positions and timed them, allowing scientists to determine the
length of the day on Venus as being equal to 243.0185 Earth days.
But, some 16 years later, surface features seen by Venus Express could only be lined
up with those observed by Magellan if the length of the Venus day is on average 6.5
minutes longer than what Magellan measured.
At first, they thought they had made a mistake because the Magellan measurements were very
accurate and they knew those were right, but after rechecking things, they still found
things did not line up.
So what's causing it to slow down? Recent atmospheric models have shown that the planet
could have weather cycles stretching over decades, which could lead to equally long-term
changes in the rotation period. Other effects could also be at work, including exchanges
of angular momentum between Venus and the Earth when the two planets are relatively
close to each other.
Finally, the UK Infrared Telescope in Hawai'i, called UKIRT, has discovered the coolest brown
dwarf yet.
But what has astronomers excited is its very peculiar colors, which make it appear either
very blue or very red, depending on which part of the spectrum is used to look at it.
The object is known as SDSS1416+13B and it is in a wide orbit around a somewhat brighter
and warmer brown dwarf, SDSS1416+13A. The brighter member of the pair was detected in
visible light by the Sloan Digital Sky Survey. By contrast, SDSS1416+13B is only seen in
infrared light. These guys are located between 15 and 50 light years from us.
OK, now I don't want to hear anything from you guys in the UK if I screw this up...
Dr Philip Lucas of the University of Hartfordshire’s
See, I had to ask somebody how to say that because here in the U.S., we want to say that
Hertfordshire, but that probably sounds like fingernails on a chalkboard to you guys and
would drive you crazy, but my experience has always been that English towns never sound
like how they're spelled, so I knew I should ask before I said it. I hope I got that right,
I don't want an avalanche of comments about that. Where the heck does Hart come from,
it's spelled Hert, H.E.R.T.
Dr Philip Lucas of the University of Hertfordshire’s School of Physics, Astronomy and Mathematics
says, "This is the fourth time in three years that UKIRT has made a record breaking discovery
of the coolest known brown dwarf, with an estimated temperature not far above 200 degrees
Celsius. We have to be a bit careful about this one because its colours are so different
than anything seen before, that we don't really understand it yet. The colours are so extreme,
that this object will keep a lot of physicists busy trying to explain it."
The strange colors nay come from their age. It seems that both brown dwarfs, dwarves?,
are somewhat poor in heavy elements. This would be consistent with the pair being old,
which in turn implies a high gravity for both dwarfs, which can further enhance the unusual
colors that were seen for both of them.
Didn't I tell you that the future was in the infrared? Huh? Yes, I think I did. If you're
taking notes, I think you'll find that most of the exciting discoveries in astronomy these
days is being done in the IR.
IR Telescopes let us see into the heart of our galaxy, measure temperatures of all kinds
of things, and help us find little brown dwarves.
And that is just like downtown.
Well, that's it for this week Space Fans, thank you for watching, and as always, Keep
Looking Up!