Celebrating 50 Years of X-ray Astronomy:
Construction of an X-ray polarimetry instrument.
The future of X-ray astronomy looks very promising, scientifically
speaking. New technologies are being developed in order to glean as much
information as possible from the X-ray light we can observe. One of
these new tools is called polarimetry by measuring the
polarization of the X-ray light from as source, astronomers have another
tool for studying the shape and environment of light-emitting regions.
Joe Hill works on polarimetry instrumentation at NASA's Goddard Space Flight Center.
"[In the next 10 years] I'm hoping we'll have polarimetry as just
another tool in the toolbox, that is as commonly used as the
spectrometer or as an imager. I'm hoping that's where we go."
An illustration of how the Astro-H satellite observatory is configured.
"SXS" is the Soft X-ray Spectrometer, "HXI" is the Hard X-ray Imager,
and "SXI" is the Soft X-ray Imager. "Soft" X-rays are those with lower
energies, and "hard" X-rays are those with higher energy.
Many of our scientists are looking ahead to the
an upcoming X-ray mission in the works by the Japanese with collaboration from NASA.
"[On Astro-H] there are two prime instruments: the X-ray calorimeter
and the hard X-ray imager, and two subsidiary instruments: an X-ray CCD
telescope camera, and a soft gamma-ray detector. The calorimeter is the
one that Goddard is providing.
What's nifty about that is that in the X-ray band, we have suffered from
not having good spectral resolution with enough collecting area. So,
Chandra and XMM had breakthroughs in spectral resolution. The gratings
were much, much better than anything that came before 50 times
better, but they need very long exposures and/or very bright sources....
The nice thing about the calorimeter is that it has much higher
efficiency, so we have a lot more signal. It also has a very broad band
pass. If you look at the way gratings work, they're sort of tuned
or blazed, it's called to a particular wavelength. A calorimeter
is a very broad band pass. What's most important is that gratings only
work on things that are point-like. In a calorimeter, a photon lands on
it, and you know its position, its time and its energy, so you can take
a true spectral image. For extended sources, such as galaxies, supernova
remnants and clusters, it's the first high-resolution spectrum."
"It's a spectroscopy question. Spectroscopy has been done before,
but in a crude fashion. Astro-H increases the resolution of the
spectroscopy by an order of magnitude. Gratings have a high resolution,
but they have a low effective area. It can only look at one spectral
line at a time. It's very time-consuming. Astro-H will allow you to see
the entire spectrum at once. The resolution is commensurate with the
resolution of gratings, and we will be able to see with high efficiency
the entire spectrum at the same time. That's the first of a kind, and
opens up all kinds of possibilities.
Koji Mukai is also looking forward to the Astro-H mission, and is
excited about the progress being made there.
"We'll do some fantastic science of high-resolution spectroscopy in
X-rays. Most of the instruments have the engineering models done, and
they have been tested. Teams at Goddard and elsewhere have begun to
build the full model instrument.... We are almost at the stage of
starting full production of the instrument."
Still image from a computer animation of a spinning black hole. In this
image, the event horizon is depicted by a black sphere, while a disk of
gas surrounds and orbits the black hole. One goal of X-ray astronomy is
to image a black hole event horizon. (Credit: NASA)
When asked what their vision of X-ray astronomy was for the next 50
years, these scientists were optimistic.
"It's amazing how much we have been able to do in 50 years. In
terms of how good our instruments are today, I think we have made as
much progress as optical astronomers did since the time of Galileo the
first optical telescope to the most powerful telescope today. I think
we've come a long way, and I hope we can keep that up somehow."
"I hope we're on platforms with our detectors, and doing new
things. We had talked about putting astronomy bases on the Moon. You can
imagine going there and launching things from the Moon..., because you've got less
gravity to overcome to get it out into space. You could take it out in
pieces in a couple of SpaceX trips. Something more like the ISS, where
you're doing your astrophysics from the space station, so you've got
more people up there, and they can adjust what they do ... you can build
stuff up a little bit."
"On the 100th anniversary, my hope is that we will be taking X-ray
pictures of the event horizons of black holes. In ten years, my hope is
that we will still be developing new X-ray missions in the U.S."
"A successor to Astro-H would be needed in
order to provide comprehensive observations of astronomical sources
together with the other next generation instruments. Especially it would
enable us to continue determining the full accretion and feedback
history of active galactic nuclei over time, i.e. the evolution of the
On a time scale of 100 years, I think the best answer
regarding the status of the field of X-ray astronomy has to be that we
cannot envision it today. Turning the question around and thinking 100
years back, X-ray astronomy obviously did not even exist, and so
fundamental astronomical concepts like the expansion of the universe or
the processes inside stars were not yet known. One can speculate about
observatories that might be possible, though, and ideas that have been
mentioned are large X-ray telescopes in lunar craters or constructions
that allow for milliarcsecond resolution X-ray interferometry.
Furthermore, exciting synergies might be possible from simultaneous
observations with neutrino or gravitational wave observatories."
"The legacy that I like to think of is that the Goddard group is
important, not only in the U.S., but in the world, and being the second
member to join this group, I feel that I was there right at the
beginning of it. Within that time, and in that group, I pioneered two
types of instruments [and was part of] several missions, including XTE,
which was just decommissioned and produced a tremendous amount of data;
the other was the mirrors, that are affordable, can fly in small
spacecraft, and don't have to wait a lifetime before something like
Chandra to fly again. They have taken over where the low-resolution
proportional counters did, and continued with both timing and
spectroscopy past that point."
Publication Date: June 2012