A new view of the energetic universe

Dec 03, 2013 by Douglas Smith
A new view of the energetic universe

The Nuclear Spectroscopic Telescope Array, or NuSTAR, sees the high-energy X-rays emitted by the densest, hottest regions of the universe. The brainchild of Fiona Harrison, Caltech's Benjamin M. Rosen Professor of Physics and Astronomy and NuSTAR's principal investigator, the phone-booth-sized NuSTAR was launched from beneath an airplane's wing, unfolding to the length of a school bus once in orbit. Professor Harrison will describe NuSTAR's unlikely journey and share some of its remarkable results at 8:00 p.m. on Wednesday, December 4, in Caltech's Beckman Auditorium. Admission is free.

Q: What's "new" about NuSTAR?

NuSTAR is the first focusing high-energy X-ray telescope. X-rays can be focused by reflection, but they're so penetrating that they only reflect at very glancing angles—sort of like skipping a stone off the surface of a lake. But most of the X-rays don't interact even then, so you use "nested optics," which you can think of as a set of cones nested inside one another like Russian dolls. Each cone intercepts some of the X-ray beam. The higher the energy, the more glancing the reflecting angle is, and the more cones you need.

Other focusing telescopes, such as NASA's Chandra X-ray Observatory and the European Space Agency's X-ray Multi-Mirror Mission, observe X-rays with energies below about 10 kilo-electronvolts. NuSTAR can see up to 79 kilo-electronvolts. Chandra has four nested mirrors, each about an inch thick and set at about a one-degree angle; NuSTAR has 133 mirrors as thin as my fingernail and almost parallel to the incoming light. We developed the detector here at Caltech. It's a digital camera, but made out of a special material that stops the high-energy X-rays that would have gone straight through previous X-ray imaging detectors.

NuSTAR is hundreds of times more sensitive, and its images are 10 times crisper than its nonfocusing predecessors, which basically worked like the pinhole camera you may have used to watch a solar eclipse. So we're able to observe the universe to much greater depth and in much greater detail than has previously been possible.

Q: What does NuSTAR see that we wouldn't see at other wavelengths?

A whole variety of things.

Medical X-rays are about 60 kilo-electronvolts, which is in the band that we observe. They penetrate the skin but stop in the bones, casting a shadow that shows up on the film. Similarly, we can look into the hearts of galaxies with high-energy X-rays, which penetrate the clouds of dust and gas where low-energy X-rays would be absorbed. We can see , or rather the X-rays emitted by the very hot stuff falling into them. We can see neutron stars, which are the collapsed cores of burned-out stars so dense that a teaspoon of neutron star would weigh more than all of humanity. We can see the remnants of dead, exploded stars.

Q: What is your role in all this?

A: I built a pinhole-camera-type X-ray telescope as part of my PhD work at Berkeley in the early '90s, but I needed something much more sensitive to do what I really wanted to do. So I came down to Caltech, and we began developing NuSTAR's technology for a balloon experiment called the High-Energy Focusing Telescope, or HEFT. HEFT flew in 2005 and was so successful that we submitted a proposal to NASA's Small Explorer program to build a space version. As the principal investigator, I was responsible for putting the team together that proposed NuSTAR to NASA, and for overseeing the construction and launch. Now I lead the science team, which decides what to look at and analyzes all the data. Our primary mission ends in 2014, so right now I'm starting to write a proposal to extend the mission for another two years as a guest-investigator program open to anyone anywhere in the world.

I hope NuSTAR keeps me busy for another 10 years or more. There are no expendables such as cryogenic coolant, so it's a matter of how long the orbit lasts. We do experience atmospheric drag, so NuSTAR will eventually reenter and burn up. Either that, or something will break. As a small, inexpensive mission, we don't have redundant systems. If something breaks, there's no backup to switch over to.

Explore further: NuSTAR delivers the X-ray goods

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Benni
1.4 / 5 (9) Dec 03, 2013
What we are learning is that increasing spectroscopic sensitivity to ever shorter wavelengths may someday reveal whole bodies of objects we never knew existed.

There will come a point that the portion of the electromagnetic spectrum we assign to the gamma ray region will need to be re-evaluated because new scintillation detectors are detecting ever higher frequencies that are beyond the measurable range of gamma ray spectroscopy, right now we call it "dark energy" because we still can't detect & measure the wavelengths of those frequencies.

It will be in these ever higher frequency ranges we now label "dark energy" that we will begin unraveling the secrets of cosmic expansion.
Royale
1 / 5 (5) Dec 03, 2013
Benni, I hope you're right. That sounds very exciting to me.
Benni
1.8 / 5 (5) Dec 04, 2013
It will be in these ever higher frequency ranges we now label "dark energy" that we will begin unraveling the secrets of cosmic expansion.


Is this the stuffs they are talking about when they talk about the dark energy stuffs? They just don't have the right satellites to see it very well? If that is right, why aren't they sending up the right kind of satellites to see it?


They need scintillation detectors that are more sensitive for measuring higher frequency ranges than what we have today. Every once in a while in our lab we replace our gamma spectroscopy equipment due to equipment breakdowns. Whenever we upgrade the scintillation detectors we discover we are able to measure a slightly increased range of frequencies into the gamma ray region, this is because the manufacturer has improved their technology since the last time we bought scintillation detectors from them.

Somewhere on the EM Spectrum must come a point we recognize frequencies higher than Gamma.
Ottoisapig
1.6 / 5 (7) Dec 04, 2013
Hey Zephir fag, does it hurt to be so stupid?
Benni
2.6 / 5 (5) Dec 04, 2013
Every spectroscopy device made has what is called its' Highest Level of Detection & conversely its' Lowest Level of Detection.

The electromagnetic spectrum does not have a wall at either end where frequencies extend only to a specific high or low wavelength & suddenly it hits a wall & comes to a dead stop. It is only the limits of instrumentation that prevent us from measuring additional higher or lower frequencies.

A few weeks ago we were in the lab calibrating a new scintillation detector & were stunned at its increased range into the gamma ray region, we'd never seen those wavelengths before. I like some of you can just imagine what they will someday be able to put aboard satellites to find previously unknown stellar bodies, unknown only because we couldn't detect their high frequency outputs with older equipment. Yep, it's becoming more & more interesting.
GSwift7
5 / 5 (1) Dec 05, 2013
The electromagnetic spectrum does not have a wall at either end where frequencies extend only to a specific high or low wavelength & suddenly it hits a wall & comes to a dead stop. It is only the limits of instrumentation that prevent us from measuring additional higher or lower frequencies


Doesn't quantum mechanics demand that there actually is a finite limit to the max and min frequency? QT suggests that there is an amount of time so small that it cannot be divided further. If so, you couldn't reach a frequency faster than 1/x, where x is that single quanta of time. The same thing would apply to extremely long wavelengths, but limited by the minimum wave energy of a single photon before it would have to become zero. (that's according to QT anyway)
Benni
2.6 / 5 (5) Dec 05, 2013
The electromagnetic spectrum does not have a wall at either end where frequencies extend only to a specific high or low wavelength & suddenly it hits a wall & comes to a dead stop. It is only the limits of instrumentation that prevent us from measuring additional higher or lower frequencies


Doesn't quantum mechanics demand that there actually is a finite limit to the max and min frequency?


HI Swift, relevant point and I clearly see it, however it is only my personal opinion your point may be the case. My experience in this area is strictly limited to nuclear/electrical engineering, we never get into QT because there is no application for it in product design, whatever works is all we care about.

But like you, I do my best in keeping up with the theories behind why things work the way they do. It is not unreasonable there is a limited range of the EM Spectrum, after all the Universe as we know it had a beginning of some kind, such precludes an infinite EM Spectrum.
GSwift7
not rated yet Dec 06, 2013
It is not unreasonable there is a limited range of the EM Spectrum, after all the Universe as we know it had a beginning of some kind, such precludes an infinite EM Spectrum


Yeah, not unreasonable, and the concept actually arises as a consequence of other first principle theories, including thermodynamics. I'm still not 100% sold on QT though, no matter how reasonable it seems in some ways. I don't support any alternative either, so I guess I'm an equal opportunity hater, lol. It just seems like we aren't quite there yet, in terms of finding the correct theory. I think maybe it's like an onion, where we need to peel back another layer in order to see the layer beneath. The answer is probably 42, and that would explain a lot of things, haha.

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