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SYFY WIRE Bad Astronomy

“Amateur” Digs Deep—Very Deep—Into an Active Galaxy

By Phil Plait

Centaurus A (or Cen A to its friends) is a nearby galaxy with a weird history. Itâs an elliptical galaxyâa giant cotton ball collection of starsâthat was, until recently, two separate galaxies that collided and merged. It has a huge dust lane cutting right across the middle, a sure-fire sign that the galaxy was the result of a cosmic train wreck.

Amateur astronomer Rolf Olsen sent me a note the other day, telling me he had taken an image of Cen A. And itâs not just any image: Itâs the result of a shocking 120 hours of total exposure! Itâs a jaw-dropping view of this iconic galaxy:

Holy Haleakala!

The detail is amazing, and you really seriously want to embiggen it; I had to shrink it a lot to fit it on the blog. Going over the details at Olsenâs site just amazed me more and more.

[Update (June 8, 2013 at 17:00 UTC): Olsen added his image to another, wider-field image taken by astrophotographer Mike Sidonio, showing even more structure in the galaxy in the outskirts. The result is astonishing.]

First and foremost: He took these images with a 25 cm (10â) telescope that he made himself. Thatâs incredible. A âscope that small is not one youâd think you could get this kind of image with, but persistence pays off. It took a total of 43 nights across February to May of 2013 to pull this picture off.

The features you can see are astonishing. The galaxy has a massive central black hole, and is actively gobbling down matter (which is why itâs called an active galaxy). You canât see the black hole itself, but blasting away from the black hole at a good fraction of the speed of light are a pair of jets, beams of matter and energy heading in opposite directions (I describe how these form in detail in a post on Herc A, another active galaxy). Olsenâs image easily captures the inner jet on the side of the galaxy facing us:

On the left is Olsenâs shot, and on the right one from a 2.2 meter telescope. Obviously, the bigger âscope has far higher resolution, and can see fainter stars and features in the jet, but Olsenâs shot is pretty impressive.

In the big picture you can also see the shells of gas surrounding the galaxy, which are probably remnants of the collision, which sent out vast waves of material like ripples from a rock dropped in a pond. He was also able to identify over 700 globular clusters in his imageâthose are tight, spherical clusters of stars that orbit most galaxies. The Milky Way has over 150, but Cen A may have ten times as many.

Cen A is pretty close, just 12 million light years away, making it the nearest active galaxy to us, and one of the brightest in the sky. Itâs best visible from the southern hemisphere, making it a juicy target for Olsenâs New Zealand location. Still, using a ten-incher to take an image this deep and detailed is a daunting task, so I encourage you to read how he did it. Iâll add that a few years back he contacted me to say he had actually seen the debris diskâthe leftover planet-forming materialâaround the star Beta Pictoris. No amateur had ever done that (it was only discovered in the 1980s!), so I was very skeptical. But his image and methods checked out; it was an incredible acomplishment. Itâs clear he is very skilled and extremely dedicated. To say the least.

I canât even imagine what heâll try next. But whatever it is, I know it will be worth keeping an eye on his efforts.

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