Hello Space Fans and welcome to another edition of Space Fan News.
If you’re a space fan like me (and I know you are cuz you’re here), then you’re
very interested in keeping up to date on the latest from the Event Horizon Telescope.
This is a worldwide collaboration of astronomers and observatories from around the world that’s
using the Earth as a primary mirror in a telescope designed to directly image the black hole
at the center of our galaxy known as Sagittarius A Star.
As most of you are aware by now, there is a massive black hole at the center of our
galaxy that astronomers lovingly call Sagittarius A star.
Sagittarius because it’s located in the constellation Sagittarius, A, because it’s
the brightest radio source in that constellation and Star because it was exciting - hold on
- not that kind of exciting, excited states of atoms!
And they are denoted in radio sources with asterisks.
This black hole weighs in at four million solar masses but because it’s located directly
smack-dab in the middle of the Milky Way, it’s really hard to see through all the
junk in the way.
Well technology has finally gotten to the point where it’s possible using millimeter
wave telescopes to directly image the silhouette - or shadow - of the event horizon against
the background radiation of material in the accretion disk of material falling into the
black hole.
Using telescopes in combination that yields an objective the size of the Earth means that
there are two black holes that can now be directly resolved with a telescope of that
size: Sagittarius A star and the black hole at the center of the galaxy M87
As I’ve reported in the past, the member telescopes that made up the Event Horizon
Telescope took data in April of last year from the eight telescopes that will be used
to derive the image of the event horizon.
They looked at both Sag A* and M87 for a week.
They took so much data that it couldn’t be reliably transferred over the internet
so they gathered it all up on hard drives and sent it to computing centers to start
crunching the numbers.
So, where are we now?
What’s the status and where’s that image?
By now everyone’s gotten the hard drives and they are trying to fit the data using
models to get the image.
The disks from the South Pole telescope arrived late last year because the station shuts down
for the winter which caused some delays but now that all the data are in, they are working
on the image.
Why does this take so long?
The EHT team has spent many months first studying the combined data to make sure that all the
detrimental effects that could degrade the event horizon image are fully understood.
These effects include turbulence in the Earth’s atmosphere as well as random noise and spurious
signals added by our own instrumentation.
It also takes a while because they got interrupted.
Last month, they re-imaged Sag A* a second time to build up the signal and now they are
working on getting that data back and into the mix.
They can only do these observations once a year because of the geometry of the center
of the galaxy and the telescopes on Earth.
And they can do this indefinitely, with each annual pass getting a better signal to build
up the image with.
The EHT team plans to observe Sag A* and M87 each year but to do that, they had to built
up over the past year a robust framework that allows the EHT scientists, from over 12 countries
and 30 institutes, to work together on instrumentation, observation, theory and simulations.
It’s also worth mentioning that a paper came out this month announcing that there
was evidence of an asymmetric source measuring roughly three Schwartzchild radii (that’s
a measure of the size of a black hole) seen in March 2013 using six VLBI stations in Hawaii,
California, Arizona, and Chile.
This observation was a precursor to the EHT observations and is consistent with the predicted
size of Sag A* by General Relativity to be two and a half Schwartzchild Radii.
According to the Event Horizon Telescope Blog, preliminary images will begin to come out
over the coming months and the signatures for the orbiting material around the black
hole will be conducted, making this among one of the most exciting things to look for
in the world of astronomy this year and in the years to come.
You know, it’s really quite amazing, General Relativity predicts the existence of black
holes, and we’ve inferred their existence just like we do with dark matter, by looking
at the effect of black holes on things we can see, like gamma ray jets from accelerating
particles falling in and stuff like that.
But we’ve never directly seen one, and looking at the shadow of the event horizon against
the backdrop of destruction that is a black hole, will be direct proof that black holes
do indeed exist.
Please check out this cool video made by the Harvard guys outlining what the Event Horizon
Telescope is and how it works.
If you don’t know much about it, it’s well worth a watch.
Well, that’s it for this episode Space Fans, thanks so much for all your support in keeping
Deep Astronomy alive, especially these guys.
Thanks to all of you for watching and as always, Keep Looking Up!