Wednesday, 9 September 2009

Hubble opens its eyes!

Our beloved Hubble Space Telescope has fully recovered from surgery, I mean servicing missions, and sent us back a huge bulletin of incredible images released today. At least two galaxies already known on the Galaxy Zoo Forum are among them, so besides hearing more about Hubble, we've another excuse to get terribly excited as usual!

One is ARP 185. Here is the Sloan Digital Sky Survey picture:

And here is Hubble's. It's worth scrolling down to look at the data, too - the narrower part is over 200,000 light years across!

We also have Stephan's Quintet, which has been Object of the Day twice on the forum, by Jules in March and Waveney last week. This is the SDSS view:

And here is the latest Hubble shot. Incidentally, there is also this older Hubble archive, just as beautiful but less detailed.

I could (and do, sometimes) show you pretty pictures for hours - but what excited me most was an elusive galaxy named Markarian 817. This has proved impossible to find on Google, Google Sky, and the Galaxy Zoo Forum. (Well, there were one or two Google links, but they didn't open on Safari or Firefox.) Hubble took its spectrum in 1997, and took it again since opening its eyes, and look - it's mostly the same, but they have one big difference . . .

(For a larger image, click here.)

A dip in the spectrum means absorbed light. The larger the dip, the more light has been absorbed. That big peak in the middle has risen until it's almost normal. That means a lot of the gas has gone.

Markarian 817 is an active galaxy, 430 million light years away in the constellation Draco. Active galaxies make up approximately 1% of all galaxies, and they are "active" because their cores shine as powerfully as can anything in the Universe: a supermassive black hole, 40 million times the mass of our Sun in Markarian 817's, is drawing in an accretion disk of material, which glows with intense heat and generates a massive stellar wind. Ironically, this means that a supermassive black hole is actually throwing a lot of gas out of the galaxy.

What has happened in this case is that the gas has moved in the last 12 years. Hubblesite writes: ". . . [T]he cloud has apparently been driven out by an outflow of material from the galaxy . . . The disk is driving the material out of the galaxy through powerful winds, produced by streams of charged particles. Some of the outflow rains back onto the galaxy. The rest settles into the intergalactic gas.

"Astronomers want to know how much of the outflow lands in the galaxy and how much escapes into intergalactic space."

I'd love to know that too - it certainly has implications for my own interests, such as the Irregulars project and galaxies which seem to have beyond-greenbelt-suburbs. How much gas is available to each galaxy determines its colour and its star formation. It almost starts to look as if galaxies are performing a sort of unintended gas exchange! Of course, the galaxy might draw its own gas back and carry on powering that active galactic nucleus for many billions of years to come.

I wonder what the spectrum will look like in another 12 years? Or twelve hundred?

Anyway, it's wonderful to see Hubble back in full "health" again. People are suffering from euphoria quite as badly as the Hypervelocity Star team. "Astronomers declared NASA's Hubble Space Telescope a fully rejuvenated observatory," announces Hubblesite. Keith Knoll, team leader at the Space Telescope Science Institute in Baltimore, is reported as saying: "We couldn't be more thrilled with the quality of the images," and "The telescope was given an extreme makeover and now is significantly more powerful than ever, well-equipped to last into the next decade." And David Leckrone at NASA's Goddard Space Flight Center: "Prior to this servicing mission, we had only three unique instrument channels still working, and today we have 13. I'm very proud to be able to say, 'mission accomplished.' "

I love it when scientists get so jubilantly excited. Science is something one is never too old to find exhiliarating. Hubble is a great favourite for both scientists and the general public, too - Leckrone wrote movingly in the introduction of "Hubble: The Mirror on the Universe" (June 2007) that every member of the public who asks him his job is fascinated to hear about Hubble, and really wants it to be "saved". Not only because of its beautiful images; not only that these images are available to everybody; but because "we as human beings can take justifiable pride in the fact that we have created and used Hubble for entirely peaceful purposes in a world that suffers continuous conflict and pain. Hubble is noble. And we made it!"

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