Galaxy – astroengine.com

M87’s Obese Black Hole: A Step Closer to the Event Horizon Telescope

The M87 black hole blasts relativistic plumes of gas 5000 ly from the centre of the galaxy (NASA)

Fresh from the Department Of I Really Shouldn’t Have Eaten That Last Binary, astronomers attending the American Astronomical Society meeting in Seattle, Wash., have announced a supermassive black hole residing inside the nearby galaxy M87 has a weight problem.

In fact, this galactic behemoth is obese.

With a mass of 6.6 billion suns, it is the biggest black hole in our cosmic neighborhood. “It’s almost on top of us, relatively speaking. Fifty million light-years — that’s our backyard effectively. To have one so large, that’s kind of extreme,” astronomer Karl Gebhardt, with the University of Texas at Austin, told Discovery News. The black hole’s mass was arrived at after Gebhardt’s team tracked the motions of the stars near the black hole using the Gemini North telescope in Hawaii. By analyzing the stars’ orbits, the mass of the black hole could be calculated.

Although it’s been known for some time that M87’s black hole might be slightly on the heavy side, 6.6 billion solar masses exceeds previous estimates.

Previously on Astroengine, I’ve discussed the exciting possibility of imaging a black hole’s event horizon. Radio astronomers have even modeled what they might see should a collection of telescopes participate in event horizon astronomy. Naturally, to see the shadow of an event horizon, the black hole a) needs to be massive, and b) relatively close. The first nearby supermassive black hole that comes to mind is our very own Sagittarius A* (Sag. A*) that camps out in the middle of the Milky Way. That would be a good place to point our first event horizon telescope, right?

Think again. Even before astronomers were able to pinpoint M87’s black hole mass, in 2009, researchers from the Max Planck Institute and University of Texas had estimated M87’s mass to be 6.4 billion suns. Although M87 is a whopping 2,000 times further away from Earth than Sag. A*, due to its mass, the M87 supermassive black hole event horizon shadow should appear bigger in the sky than Sag. A*’s. Today’s announcement is bound to stimulate efforts in the quest to directly image a black hole’s event horizon for the first time.

“Right now we have no evidence that an object is a black hole. Within a few years, we might be able to image the shadow of the event horizon,” Gebhardt added.

For more on today’s news, read Irene Klotz’s report on Discovery News: “Obese Black Hole Lurks in Our Cosmic Backyard“

Astroengine Gets Quoted in National Geographic

The December 2010 edition of National Geographic

A couple of months ago I was contacted by National Geographic magazine notifying me that one of their writers had quoted me in an article for their December issue. Pretty cool, I thought. But then I forgot all about it.

Then, I received a note from the ever watchful Bill Hudson (@2012hoax) telling me Astroengine had been printed on page 99. I quickly scurried over to the National Geographic website to find, sure enough, I was there too: on page 3 of the online article “Star Struck.”

The following morning, I received a complementary copy of the December edition so I could see Astroengine in print for the first time.

National Geographic’s special feature takes a fascinating tour of the Milky Way and when discussing metal-poor stars in the outermost reaches of our galaxy, the article quotes the title of the Astroengine post “Life is Grim on the Galactic Rim.” Obviously they like my rhyming skills.

Thank you National Geographic!

I’ve been told I can write a blog with an excerpt from the superb article written by Ken Croswell, so that’ll be coming right up!

I think I need to blog more…

Star Birth Dominates Energy Production in Ultra-Luminous Galaxies

Artists impression of an ultra-luminous galaxy heating the surrounding dust (JAXA/ISAS/LIRA)

In the early 1980’s, NASA’s Infrared Astronomical Satellite (IRAS) detected a number of unknown objects lurking in the depths of the cosmos.

At the time, these IRAS objects stirred speculation in the press. Were the infrared signals being emitted by comets inside the Solar System? Or were they failed stars (brown dwarfs) lurking beyond the orbit of Pluto? The latter theory spawned the idea that the hunt for Planet X was back on (stoking the smoldering conspiracy embers of the flawed doomsday theory that Nibiru is coming to get us). Alas, it was neither, these intense infrared signals were coming from much, much further away.

It turned out that the infrared emissions were being generated by galaxies that, bizarrely, had little optical signal. Although a high proportion of them were known to be interacting galaxies (i.e. they were colliding with other galaxies), the exact energy mechanism driving their emissions was not known.

Ultra-luminous galaxies have the luminocity of a trillion Suns, whereas our galaxy has the luminosity of a pedestrian ten billion Suns. Obviously, ultra-luminous galaxies are different animals to the Milky Way, but a galaxy is a galaxy and the energy sources are similar whether they are ultra-luminous or not. It would appear that the only difference is how active the galaxy is.

The first obvious energy source in a galaxy is star formation; the more stars that are forming, the brighter the galaxy. Secondly — as with our galaxy — the central supermassive black hole’s accretion rate contributes to the galaxy’s energy budget; the more matter being accreted by the black hole, the more energy is being generated (and therefore the brighter the galaxy).

So, when observing these ultra-luminous galaxies, surely it should be an easy task to work out where all this energy is coming from? Actually, this isn’t the case, astronomers are having a difficult job in understanding the nature of IRAS galaxies and the reason for this comes from the source of the infrared emissions. Galactic dust is being heated by the energy source, but this dust obscures the source of this heating (it is opaque to optical wavelengths).

Smithsonian Astrophysical Observatory (SAO) researcher Guido Risaliti and his team have been analyzing Spitzer data to try to characterize the infrared emissions from 71 ultra-luminous galaxies. Using a “dust emission diagnostic technique,” the team have deduced that approximately 70% of the galaxies have active nuclei (i.e. their supermassive black holes have high accretion rates). Although most of the galactic nuclei are active, it is star formation that dominates the energy production in two-thirds of the galaxies. Also, these account for the highest fraction of the brightest galaxies.

This is a significant finding as it demonstrates how a galaxy reacts when it interacts with another galaxy. It would appear that the black hole in the core of the galactic bulge is kick-started during the massive gravitational interaction, boosting energy output as it eats more matter. The interaction also boosts star birth and this energy source becomes a dominant factor. Both energy sources heat up interstellar dust, making the galaxy glow in infrared wavelengths while optical light is masked.

Source: SAO (Harvard)

The Space Station Flares, Again!

I don’t usually post two identical stories within a few days of one another, but when I saw this image on SpaceWeather.com I had to comment on it. On Friday, I was captivated by the astounding astrophotography by Nicolas Biver as he tracked the space station with video camera and telescope, to capture some great detail of the manned outpost as it passed over France. With a bit of luck and a whole world of skill, Biver observed a bright space station flare.

Next up, it’s the turn of Martin Gembec. On May 2nd, he grabbed this superb trail as the station passed through the distinctive edge-on disk of our galaxy over the Czech Republic. What’s more, the station flared as its huge solar arrays reflected sunlight through Gembec’s ‘scope… right at the moment when the station travelled through the hazy starlit disk of the Milky Way.

The ISS flares as it passes through the Milky Way's disk (©Martin Gembec)

“We were watching a bright flyby of the space station when the ISS surprised us with a big flare in the Milky Way,” said Gembec. “At maximum, the ISS reached magnitude -8.”

A magnitude of -8 makes this flare a beast; that’s 25× brighter than Venus and 400× brighter than the star Sirius.

In the photo above, there is a rather ominous piece of kit attached to a boom reaching into the centre of the image. This is a reflection of Gembec’s Canon 30D camera (that took the picture as the ISS passed overhead) in an all-sky mirror. The mirror is in a concave shape to collect the starlight from the sky, bouncing the light into the camera lens. It acts much like a satellite dish; except it doesn’t bounce and focus radio waves into an antenna, the all-sky mirror reflects visible light and focuses it into the open camera shutter. As you can see, the results are visually stunning.

Source: Space Weather