Hubble Directly Images Disc Around a Black Hole

An anonymous reader sends this excerpt from the HST site: "A team of scientists has used the NASA/ESA Hubble Space Telescope to observe a quasar accretion disc — a brightly glowing disc of matter that is slowly being sucked into its galaxy's central black hole. Their study makes use of a novel technique that uses gravitational lensing to give an immense boost to the power of the telescope. The incredible precision of the method has allowed astronomers to directly measure the disc's size and plot the temperature across different parts of the disc."

Re:Brilliant

[EngrBohn]

Alas, we have no way to conduct servicing missions to maintain HST. Sooner or later, it will have to be decommissioned.

Re:Brilliant

[Kjella]

Well, the effect has been known since 1979. It's just that everything lines up very rarely, it's amazingly effective when it works but you can't exactly move the lens so you only get to focus on what's exactly behind it. We are going to need bigger and better telescopes to solve the general case.

Re:Could this be done from the ground?

[Carnivore]

You're right in all of your suppositions. (Except for cloudy day--It's the cloudy nights you have to watch out for :)

Today's 10m class and tomorrow's 30m class telescopes can do a lot of what Hubble has done, especially when you factor in advanced AO systems like the one that was recently installed on Gemini South (one 50W laser split into 5 beams for correction over a large field). Anything on the ground is cheaper than in space.

Hubble, JWST, Chandra, and the others can see wavelengths that are absorbed by the atmosphere, no matter how high you are.

And integration time is a huge factor. The Ultra Deep Field image was over 1.1 million seconds of exposure. It's just not practical to do exposures like that from the ground.

Re:Could this be done from the ground?

[wierdling]

I process data from the Hubble and also from the ESO Southern Observatory. And that images (and hence data) from the Hubble are still very much clearer than what the ESO SO can take. Not having to look through an ocean of air makes a huge difference.

Re:Could this be done from the ground?

[Anonymous Coward]

Since Hubble was launched, advances in adaptic optics have made it possible to capture images of similar quality from the ground. However, there is a trade-off. The nature of adaptive optics means that they are very good for imaging small regions of the sky. This is great if you want to examine a specific object with pinpoint accuracy. However, adaptive optics isn't good if you want to survey large areas of the sky - a space-based telescope such as Hubble is still the best choice for that kind of work. So it's really a question of what kind of science you want to do. For some sorts of work, ground-based telescopes are the way to go. For others, a space-based telescope allow you to perform work that wouyld take years from the ground in a fraction of the time.

However, keep in mind that adaptive optics didn't become common in astronomy until the late 1990s (although the theory was known since the 1950s).

Also, note that telescopes greater that 8m in diameter need to use a second technology known as Active Optics to correct for tiny deformations in the mirror caused by temperature changes - without this technology it is impossible to build telescopes much wider than 6-7m in diameter. This technology became available in the late 1980s and is the main reason why larger ground-based telescopes are becoming more common now.

So Hubble was launched only a few years before ground-based telescopes started to catch up with some of its capabilities - but it still has a few tricks up its sleeve that they find it hard to match.