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astronomy

HST’s Next

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The Final Servicing Mission for a Venerable Telescope

The Hubble Space Telescope
HST during a 2002 refurbishing mission.

The folks down at the Kennedy Space Center are getting ready to move space shuttle Atlantis out to the pad, in preparation for the May 12 mission to service the Hubble Space Telescope. The crew includes two astronauts who have visited HST before: John Grunsfeld (who has visited HST twice) and Mike Massimino (who is making his second trip to the telescope). They’ll be replacing and repairing faulty components in HST and putting in new science instruments.

The first is the Cosmic Origins Spectrograph (COS) (designed by folks in the Center for Astrophysics and Space Astronomy (CASA) at the University of Colorado (my alma mater for both my degrees) and Ball Aerospace), which will be focusing on light streaming from extremely distant quasars (for example) and studying that light to understand the gases that lie between us and those quasars. It reminds me of egg-candling — a process that I learned as a kid on my grandparents’ farm. You hold up an egg to a light (a candle) and the light streaming through the shell (which is fairly porous to light) highlights what’s inside. We did this to check to see if an egg had been fertilized and had a chick growing inside it. In the case of COS, it will take the light flowing through the gas clouds and dissect it into its component wavelengths. The “fingerprints” of various elements show up when you do that, and the presence of those elements (like hydrogen, oxygen, etc.) tell you something about the cloud. And its history.

The second new instrument to go into HST is the new Wide Field Camera 3 (designed and built at Goddard Space Flight Center and Ball Aerospace. It’s going to be the telescope’s imaging workhorse — and it’s sensitive to some ultraviolet and infrared wavelengths, as well as optical light.  The WFC3 and the Advanced Camera for Surveys, which is a strong optical workhorse in its own right, will work together.  Along with the repaired STIS and the rest of HST’s science complement, the observatory should be ready to go for a number of years, observing the cosmos from above the atmosphere.

It’s kind of a shock to me that the telescope has been on orbit since 1990 — nearly 20 years now.  The day it was launched, I was back in school at CU, studying astronomy and physics and thinking that I’d head into grad school for the Fudd someday. I had been working at CU’s Laboratory for Atmospheric and Space Physics on comet plasma tail studies and my boss was one of the two principal investigators for HST’s Goddard High Resolution Spectrograph. Eventually I ended up working on that team during grad school.  And, I ended up writing a book with him about the science HST was doing — a project I hatched as a graduate assignment during the dark days when HST’s spherical aberration was giving NASA a black eye.

Behind all the nasty media coverage, a handful of us knew that the telescope was still capable of doing science (albeit with some help) and that’s when I decided I wanted to bring THAT story to life –to counteract all the cutesy, nasty headlines that the media were using in place of actually delving into the truth about HST’s capabilities (even though they were degraded, we could still do work with the telescope). All the astronomy and astrophysics I was studying TOLD me what the scope COULD do, and that data could still be taken with it.  All of my journalistic and writing instincts TOLD me that there was more to the HST story than “Hubble trouble” stories.  And, here we are, nearly two decades and several servicing missions later, about to endow HST with new eyes.  It’s a heckuva story — and I’m pleased to see that it’s going to continue!

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.)