Space Fan News #65: Blazars Heat the Universe; Brown Dwarfs vs Gas Giants; Annular Eclipse

Uploaded by tdarnell on 18.05.2012

Hello Space Fans and welcome to another edition of Space Fan News.
Ever wonder what a blazar is? A blazar is a subclass of quasars, which if you'll recall
are the very bright objects associated with supermassive black holes that are emitting,
among other things, enormous quantities of gamma rays.
Blazars are powered by material falling into the supermassive black hole and galaxies that
have them are classified as having an active galactic nuclei (an AGN) and this is a very
fast growing study in cosmology.
We see blazars when their jets are pointed at us, their blinding beams outshining all
other sources. The objects are also highly variable, because their brightness is related
to material falling into a black hole, when the black hole starts to run out of stuff
to eat, the beam fades, when more stuff comes by, it gets brighter.
So that' a blazar, extremely interesting objects which should one day be the subject of a space
video, but right now, I gotta do the news.
Now it has always been thought that black holes (and their associated quasars and blazars),
could only effect their immediate surroundings: in this case, the center of the galaxy. Of
course over time, the whole galaxy might get consumed, but in this context, that's still
a pretty localized event. It would matter to the galaxy, but notsomuch the rest of the
Well, this week, a collaboration of scientists at the Heidelberg Institute for Theoretical
Studies and in Canada and the US have discovered that the diffuse gas permeating throughout
the universe - called in intergalactic medium - can absorb luminous gamma-ray emission from
black holes, heating it up. This surprising result has important implications for the
formation of structures in the universe.
The intergalactic medium is believed to contain most of the ordinary baryonic material left
over from the Big Bang. Baryonic material is a fancy word for ordinary matter.
The IGM is a very thin, diffuse gas floating throughout the universe. Astronomers estimate
the average density of the universe as a whole to be about one hydrogen atom per cubic meter,
with the intergalactic medium having about 10 to 100 atoms per cubic meter.
Because it permeates everything, it has a huge influence on things like how galaxies
formed, where they formed and how they behave once they've formed. The IGM is a record of
the entire thermal history of the universe.
Well, with this discovery, that thermal history will have to be rewritten because what they
now believe is happening is that these blazars are heating that thin gas.
Gamma rays are strange in many ways, other radiation such as visible light and radio
waves travel the universe without problems, this is not the case for high-energy gamma
This particular radiation interacts with the optical light that is emitted by galaxies,
transforming it into elementary particles like electrons and positrons.
Initially, these particles move almost at the speed of light. But as they are slowed
down by the gas in the IGM, their energy is converted into heat.
When this happens, the surrounding gas is heated quite efficiently. In fact, the temperature
of the gas at mean density becomes ten times higher, and in underdense regions more than
one hundred times higher than previously thought.
So even though the universe is expanding and cooling, the black holes are there. trying
to heat it back up again.
Next, one of the most confusing things about brown dwarf stars is telling the difference
between them and a gas giant.
I mean, Jupiter has been called both: it can be a gas giant or a brown dwarf. But which
is it? And how do you tell?
Well research from the University of Hertfordshire in the UK (man I've been talking about them
a lot lately - those scamps have been busy) has found a brown dwarf that is more than
99% hydrogen and helium.
This star is ultra-cool, it has a temperature of just 400 degrees Celsius and its discovery
could be a key step forward in helping astronomers distinguish between brown dwarfs and giant
Brown dwarfs are star-like objects with insufficient mass to ignite hydrogen fusion in their cores.
Over time they cool to temperatures of just a few hundred degrees. They form like stars
do, but they just don't get enough material together to shine.
Gas giant planets however, have a more diverse chemistry, they aren't just hydrogen because
they've accreted material, usually around a rocky core, as the solar system was forming.
This difference in chemistry is the main way astronomers discriminate between planets and
brown dwarfs. The problem is in finding them and getting their spectra. As you can imagine,
these things are hard to see directly because they are so cool.
So these guys combed through tons of survey data and developed a technique to make finding
these dim object easier. Now that they can do it, we'll finally be able to tell how many
brown dwarfs there are as well as how many gas giants.
The team detected the brown dwarf using data from the Wide-field Infrared Explorer (WISE)
satellite, the UK Infrared Telescope (UKIRT) in Hawaii and the Visible and Infrared Survey
Telescope for Astronomy (VISTA) in Chile.
The newly discovered object, known as BD+01 2920B (that's a big b), is about 35 times
more massive than Jupiter. It orbits its host star at a distance of 390 billion km or about
2600 times the average distance from the Earth to the Sun.
So now we know… what's Jupiter, a gas giant or a brown dwarf? A gas giant. And Why? Because
of the high metals and varying chemistry it has.
And finally, Space Fans in most of the U.S. will have another reason to look up this weekend.
On Sunday, there will be an annular eclipse of the Sun. The Moon will pass between the
Earth and the Sun and for a while, will be blocking part of it.
Here is where it will be visible. As you can see, I won't be able to see it here in Maryland
- which is probably just as well because I have to pack my stuff up for the move, but
most of you guys'll be able to see it.
It's supposed to start in the late afternoon and last past sunset, which means those of
you in the path will probably have some pretty neat sunsets. So try to get outside Sunday
afternoon and check it out.
I know I don't have to tell you not to stare at it because you're space fans... but don't,
you know, stare at it.
I have a link in the description box to Sky and Telescope's web page for more info so
check it out for details.
Well, that's it for this week Space Fans, thank you for watching and, as always, Keep
Looking Up.