Hello Space Fans and welcome to another edition of Space Fan News.
First up, astronomers using the Hubble Space Telescope announced this week that for the first time ever, they have directly imaged an accretion disk surrounding a black hole at the center of an active galaxy, known as a quasar.
Quasars are very distant, and are among the most luminous objects in the universe. Powered by the accretion disks of black holes, they are one of the most powerful energy sources ever seen. Most consist of a massive galaxy with a very active nucleus surrounding a central black hole.
Ordinarily objects this far away are impossible to see directly, they are too far away and our telescopes are not large enough to fully resolve them. There are about two hundred thousand known quasars in the universe and only a hand full of them are closer than three billion light years.
So how were they able to image this accretion disk?
Through our old friend, gravitational lensing, which you've heard me talk about many times.
It just so happened, when the Hubble Space Telescope was looking at a quasar known charmingly as HE 1104-1805, a galaxy passed in between us and the quasar.
The gravity from this intervening galaxy bent the light from the quasar and magnified it, just like a telescope, which increased the effective resolution of the Hubble and allowed astronomers to make some measurements.
As the galaxy moved in between the quasar and Hubble, it deflected the light in a very precise manner, deflecting different colored light which exist in different parts of the accretion disk and allowed them to make measurement of both its size and color.
The accretion disk of HE 1104-1805 is between four and eleven light-days across (approximately 100 to 300 billion kilometres). They also obtained an accurate colormap of the disk corresponding to the changes in temperature. Most accretion disks around black holes are hotter nearer the hole than farther out. With this observation, they have a detailed map if the temperature of the black hole's accretion disk.
So now, using this new gravitational lensing technique, astronomers have a way to resolve things in the sky we had no hope of ever seeing directly. They were just too far away to make out any detail.
Now we can.
Just like downtown.
Next, let's talk about the asteroid coming around next week and get it out of the way.
I've already blogged about this, but I predict we're going to get an avalanche of posts, blogs, tweets, +1's, likes and all sorts of online social networking pandemonium between now and Tuesday.
In case you don't know and you don't read my blog.... on Tuesday, November 8th, at about 6:30 eastern time in the U.S., an asteroid is going to pass within the orbit of the Moon for the first time since 1976. It will pass around 325 thousand kilometers overhead and, well, that's it.
NASA's going to watch it as it goes by.
It's going to be too dim to see with the naked eye, you'll need at least a six inch telescope to see it, and well, let's not re-invent the wheel. Here's what the guys at JPL have to say:
<JPL Video>
2005 YU-55 is going to make a very close approach to the Earth on the night of November 8, 2011. At that
time, its distance from Earth will be just under nine-tenths of the moon's distance away from us. 2005 YU-55
cannot hit Earth at least over the interval that we can compute the motion reliably which extends for several hundred years.
It's going to be moving very rapidly as it traverses the sky near the Earth on November 7, 8, 9 and 10th. In affect it'll be moving straight at us from one direction and then it will go whizzing by and straight away from us in the other direction. So its motion across the sky will be close to
degrees over the course of less than two days. It made a close approach to Earth about eighteen months ago
in April of 2010. Colleagues of ours at Arecibo Observatory where able to observe this asteroid using the
radar facility at Arecibo and they were able to obtain radar images that showed that this object is about 400
meters across. On November 8, 9, 10 we'll be observing it again.
This time with both the Arecibo telescope and with the Goldstone telescope here in California. This is the closest approach by an asteroid
that large that we've ever known about in advance. The radar telescopes that we use to observe asteroids are
very large radio dishes. The Goldstone telescope is 70 meters, which is 240 feet across so it's truly
enormous, and Arecibo is even larger still. The Goldstone telescope has a new radar imaging capability which
has just become available that will enable us to see much finer detail than has previously been possible.
And depending on how we transmit the signal we can get different types of data.
It shows us how big it is, it can show us features on the asteroid, it can tell us information about the asteroids rotation period. We
should be able to tell much better with these new observations that we're going to do.
<End JPL Video>
I really, really, really hope people don't start losing their minds over this. Let's wait and see.
Now that we have that out of the way, I want to use this flyby as an opportunity to point out that NASA operates what I consider one of its most important projects: the Near Earth Object Program.
They keep a catalog of potential hazardous asteroids, or PHA's. PHA's are currently defined based on parameters that measure an asteroid's potential to make threatening close approaches to the Earth. Specifically, all asteroids with an Earth Minimum Orbit Intersection Distance (MOID) of 0.05 AU or less and an absolute magnitude (H) of 22.0 or less are considered PHAs.
There are currently 1263 known PHA's in the solar system. Just because something is classified as a PHA though, doesn't mean it's going to hit us.
Remember that word POTENTIAL in there.
I, for one, am very grateful that program exists. Hopefully, we'll see fit to keep it funded.
Well, that's it for now Space Fans, thank you for watching and, as always,
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