Space Fan News #61: Billions of Stars; The Dust Bunnies of Fomalhaut; White Old Dwarfs


Uploaded by tdarnell on 13.04.2012

Transcript:
Hello Space Fans and welcome to another edition of Space Fan News.
Ever wondered what an image that contains a BILLION stars looks like? Well, here you
go…
Just kidding, here it is again.
Last week astronomers released an image containing more than a billion stars in our Milky Way
galaxy. This image is the result of a decade-long collaboration by astronomers at the University
of Edinburgh and the University of Cambridge to process, archive and publish the huge amount
of sky survey data generated by the UKIRT and VISTA infrared Telescopes.
Have you noticed? I seem to be mentioning VISTA a lot lately… remember the last SFN
episode, where I showed you the UltraVISTA Deep Field Image? Well, that impressed me
so much that I'm making a space video dedicated to that image.
So stay tuned!
This image however is enormous. It contains over 150 billion pixels and is really too
big for me to adequately show you in this video so I've put a link in the description
box below to a site where you can play with it and zoom and scroll around it and take
a closer look.
I'm not kidding, this thing is huge! Look, I can keep going and going and going, zooming
into this image and when I reach the point where I can't zoom anymore, depending on where
I'm looking in the image, there are STILL tens of thousands of stars.
So what's going on here is we are finally enjoying the fruits of the labors of the many
sky surveys out there at observatories around the world that have been out there night after
night, year after year, staring at wide areas of the sky. And from these individual exposures,
we add them up and we keep assembling them as more are taken to get deeper and deeper
looks into what's up there.
This image was put together by a guy you may remember from SFN #54: a guy named Dr. Phil
Lucas from the University of Hertfordshire. He is leading the UKIRT study of the Milky
Way and in that episode, I talked about his discovery of the coolest brown dwarf yet found.
I'm not gonna tell you to go watch that because I know you already have… Right?
Well here he has taken data from UKIRT (which stands for the U. K. Infrared Telescope) along
with data from the VISTA telescope and built this amazingly detailed image of the Milky
Way.
What kind of image is this? That's right, it's and infrared image, and what did I say
about that?
The future of astronomy is in the infrared.
Get used to it. I'm gonna keep rubbing it in till I get an amen from you people.
Alright, next ESA's Herschel Space Telescope - another Infrared telescope I might add - has
looked very closely at a ring of dust surrounding the star Fomalhaut.
Fomalhaut is a young star, just a few hundred million years old, and twice as massive as
the Sun. This dust belt was discovered in the 1980s by the IRAS satellite, but Herschel’s
new images of the belt show it in much more detail at far-infrared wavelengths than ever
before.
The Herschel data show that the dust in the belt has the thermal properties of small solid
particles, with sizes of only a few millionths of a metre across.
But this is a problem because the Hubble Space Telescope observations showed that these grains
of dust to be more than ten times larger.
So what we're looking at here - and the reason we can see this ring at all - is light from
the star bouncing off of the grains and hitting our detectors. As the starlight is reflected
- or more accurately - scattered by the grains, from the way it is scattered, we can learn
something about how big they are.
Observations using Hubble's filters suggested they were large grains because the ring was
dim at Hubble's wavelengths, but at slightly longer wavelengths than Hubble, Herschel found
that the thermal properties (in other words, the temperature) of the belt suggested that
the dust grains were much smaller.
So one instrument says they're big, another says they're small.
Who's right? What can explain large grain sizes seen in Hubble at a temperature that
suggests small grains as seen by Herschel?
Well, these guys are suggesting that the dust grains must be large fluffy aggregates of
dust, or dust bunnies if you will, similar particles released from comets in our own
Solar System.
So this stuff is from comets, that's cool.
And there's bunnies!
But this presents another problem: the radiation from Fomalhaut should blow away the puffy,
fluffy dust bunnies, but they are still there.
Well, what may be happening is that there are continuous collisions between the comets
in orbit around Fomalhaut, constantly creating new dust bunnies.
And to sustain the belt, to keep replacing what is blowing away, the rate of collisions
must be huge: each day, the equivalent of either two 10 km-sized comets or 2000 1 km-sized
comets must be completely crushed into small fluffy, dust bunnies.
That's every day.
And what's more, to keep the collision rate that high and sustain it for any length of
time, there would have to be a supply of between 260 billion and 83 trillion comets in the
belt to smash into each other!
That's a lot of comets.
And a lot of dust bunnies…
For reference, our own Solar System has a similar number of comets in the Oort Cloud,
which formed from stuff scattered from a disc of material surrounding the Sun when it was
as young as Fomalhaut.
So this is probably the precursor to Fomalhaut's Oort Cloud.
Finally, astronomers from the University of Oklahoma have found some really old white
dwarf stars, and they're right next door.
OK< let's see if I can do this.
These stars, known as WD 0346+246 and SDSS J110217, 48+411315.4 respectively are 100
light years away and are in the constellations of Taurus and Ursa Major.
They are 12 billion years old folks. The universe was just a baby.
So how do they know how old they are? White dwarfs are formed when a star, like our Sun,
(our sun will dies this way) begins to shed it's outer layers of gas into a planetary
nebula.
This star isn't fusing elements anymore, it's what's known as a degenerate core.
But setting aside its morals for the moment. Sorry, bad joke. Couldn't help myself.
The material in the white dwarf no longer undergoes fusion so it has no source of energy.
Since there is no energy from fusion to hold it up, it is kept from collapsing by something
called electron degeneracy pressure, which says that no electron can occupy the same
space at the same time and this prevents collapse and causes the white dwarf to be extremely
dense.
So the star doesn't shine as much as glow and it slowly cools over time at a rate we
know. Knowing how cool a white dwarf is allows us to run the clock backward to when it was
the temperature of a brand new white dwarf, and this leads us directly to its age.
Well, that's it for this week Space Fans, as always, thanks for watching and Keep Looking
Up!