Category Archives: black holes

black holes

A Black Hole Gets the Vapors

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There’s Water Out There — WAY Out There!

You know that stuff that falls out of the sky, runs through rivers, fills the oceans, makes up ice cubes here in our refrigerators on Earth? That water stuff?  Well, it can be found in some pretty distant reaches of the cosmos, not just here on good ol’ planet Earth (or locked away on a Martian polar ice cap or under Europa’s shimmering icy surface). Astronomers have found signs of water in a very distant part of universe. It’s actually water vapor contained in a jet ejected from a supermassive black hole that lies billions of light-years away from us.  That water vapor existed near the black hole at a point about 2.5 billion years AFTER the Big Bang. That is an incredibly long time ago, and shows us the scene at a time when the universe was still quite young.

The black hole is jackhammering out of a galaxy called MG J0414+0534, and what the astronomers saw was the telltale fingerprint of water vapor in emissions from something called a maser. This is a region of gas where molecules in the gas amplify and emit beams of microwave radiation in much the same way as a laser emits beams of light. For it to show the fingerprint of water vapor scientists detected means that the gas-emitting region is hot and dense enough to heat water to its boiling point.

The image is made from HST data and shows the four lensed images of the dusty red quasar, connected by a gravitational arc of the quasar host galaxy. The lensing galaxy is seen in the center, between the four lensed images. (Courtesy John McKean/HST Archive data. Click to embiggen.)
This image is made from HST data and shows the four lensed images of a dusty red quasar (which contains the jet and water maser emissions), connected by a gravitational arc of the quasar host galaxy. The lensing galaxy is seen in the center, between the four lensed images. (Courtesy John McKean/HST Archive data. Click to embiggen.)

This water maser emission is not something you can see with an optical telescope. You need radio telescopes like the Extended Very Large Array and the Effelsberg radio telescope that can detect the emissions, and you need a gravitational lens. The gravitational lens acts as if it was a telescope, bending and magnifying light from the distant galaxy to make a clover-leaf pattern of four images of MG J0414+0534.

The detection of water in the early universe poses a lot of questions for scientists who want to understand what happened back in the infancy of the cosmos.  The existence of the water vapor near this particular galaxy core and its black hole could mean that there is a higher abundance of dust and gas around the super-massive black hole at this time in the galaxy’s existence.

Or, it could be because the black holes were more active at that time, leading to the emission of more powerful jets that would set up the conditions for water masers to exist and emit their radiation.  One thing that scientists are sure of as they study this data: the water vapor must be very hot and dense in order for it to even be detected.  That is spurring astronomers to figure out just what it is that is causing the gas to be as dense as it is.

Want more details about this amazing find? Check out the press release at the Royal Astronomical Society web site.

astronomy, black holes, blazar, Fermi/GLAST, galaxies, HESS, RXTE

Exploring the Mighty Blazar

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Looking into the Active Heart of a Galaxy

In the cosmic zoo of interesting things “out there”, blazars are right up there with neutron stars and gamma-ray bursters as astrophysically interesting objects. What are these blazars? Think of galaxies out there that have active cores — those regions are often referred to as active galactic nuclei. Such a place is busily pouring out radiation at nearly every wavelength and some are particularly bright in the x-ray, radio, and gamma-ray regimes. This is  happening because there’s a supermassive black hole at the center, gobbling up material and belching out radiation and emitting a jet that threads its way through an intensely twisted magnetic field.

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Blazars are very compact (tightly squeezed into a comparatively small area of the galaxy), they appear to be highly variable in their output, and as it turns out, their jets are pointing in our general direction.  So, when we look at a blazar, we are essentially looking along the long axis of the jet back “down” toward its source — which is presumably toward the black hole and its accretion disk.

Astronomers want to look at blazars in various wavelength “regimes” to understand the structure of these cosmic power plants. Different structures and activities radiate at different wavelengths. Recently an international group of astronomers looked at the galaxy PKS 2155-304, which is about 1.5 billion light-years away (relatively close, for a galaxy) and is a regular source of faint gamma-ray signals. Now, if you see gamma rays, you know there’s something really active going on, and when you see a gamma-ray source brighten and then dim down, you know you’ve got something interesting happening there. So, when PKS 2155-304 brightened up in 2006, the astronomers took a look it with optical (visible-light), x-ray, and gamma-ray telescopes to capture its “light signature” in as many wavelengths as they could.

The H.E.S.S. telescope in Namibia.
The H.E.S.S. telescope in Namibia.

Between August 25 and September 6, 2008, astronomers used several telescopes to monitor PKS 2155-304 as it was quiet and giving off no flares. They used the  Large Area Telescope (LAT) aboard NASA’s orbiting Fermi Gamma-ray Space Telescope to look for gamma-ray emissions. X-ray emissions were detected using NASA’s Swift and Rossi X-ray Timing Explorer (RXTE). Rounding out the wavelength coverage was the H.E.S.S. Automatic Telescope for Optical Monitoring, which recorded the galaxy’s activity in visible light.

What they found out about PKS during both its flaring and quiet states tells them something about the central engine. But what? During flaring episodes of this and other blazars, the x- and gamma-ray emission rise and fall together. However, when PKS 2155-304 is in its quiet state, the same two emission regimes do not seem to rise and fall together. Why this is is till a mystery. What’s even stranger is that the galaxy’s visible light rises and falls with its gamma-ray emission. One of the scientists on the team, Berrie Giebels, described it like this:  “It’s like watching a blowtorch where the highest temperatures and the lowest temperatures change in step, but the middle temperatures do not.”

So, the black hole engine at the heart of PKS 2155-304 is doing something, and the next step is to find out what. Clearly there’s something periodic going on as it gobbles up material in the accretion disk. Are there clumps in the accretion disk? Is there something that periodically affect the jet in some way?  Whatever it is gets “telegraphed” out in the radiation we’re seeing as the jets stream out from the action at the heart of the active galaxy. It’s not likely this will stay a mystery for TOO long, since continued observations over longer periods of time will eventually help astronomers uncover what’s going on in the middle of this blazar. (For more information on this study, surf over to NASA’s Fermi mission site.)