NASA rocket mission probe seeks source of X-rays from inner galaxy

This image shows a “map” of the night sky in soft X-ray light in galactic coordinates, with the sun at the center. The horizontal line in the center of the image runs along the plane of our disk-shaped galaxy. University of Wisconsin, Madison astronomer Dan McCammon and the XQC team will observe the bright blob in the center of the image, circled with a dotted line. This is the southern part of a roughly circular blob around the center of the galaxy, bisected by cold absorbing gas in the plane of the galaxy. Credit: Snowden et al., 1997

To human eyes, the night sky between the stars appears dark, the emptiness of space. But X-ray telescopes capture a very different picture. Like a distant fireworks display, our images of the X-ray sky reveal a universe thriving with activity. They indicate as yet unknown cosmic eruptions that come somewhere deeper in our galaxy.

To help find the source of these mysterious X-rays, University of Wisconsin Madison astronomer Dan McCammon and his team are launching the X-ray Quantum Calorimeter, or XQC instrument. XQC will make its seventh trip to space aboard a NASA suborbital rocket. This time, XQC will detect a sliver of X-ray light with 50 times better energy resolution than ever before, key to revealing the source. The launch window opens on June 26, 2022 at Equatorial Launch Australia’s Arnhem Space Center in Australia’s Northern Territory.

Because the Earth’s atmosphere absorbs X-rays, our first observations of cosmic X-rays were waiting for the space age. In June 1962, physicists Bruno Rossi and Ricardo Giacconi launched the first X-ray detector into space. The flight revealed the first sources of X-rays beyond our Sun: Scorpius X-1, a binary star system some 9,000 light-years away, as well as a diffuse glow scattered across the sky. The discovery formed the basis for the field of X-ray astronomy and later won Giacconi part of the Nobel Prize in Physics in 2002.

This animated image shows the two alternate sources of the X-rays that the XQC mission is investigating. Credit: NASA’s Goddard Space Flight Center

Using other NASA X-ray missions, scientists have now mapped the X-ray sky in increasingly finer detail. Still, there are several bright patches whose sources are unknown. For the upcoming flight, McCammon and his team will focus on a patch of X-ray light that is only partially visible from the Northern Hemisphere.

“It covers a large part of the galaxy, but we had to be in the southern hemisphere to see that part of the sky,” McCammon said. “We’ve been waiting a long time for this expedition to Australia.”

Scientists believe the X-ray spot comes from diffuse, hot gas heated by supernovas, the brilliant outbursts of dying stars. The XQC mission investigates two possible sources, illustrated in the image below.

One possibility is that the X-rays come from gas heated by “Type Ia” supernovas, the death throes of massive stars that live for tens to hundreds of millions of years. The innermost part of our galaxy has a concentration of this type of supernova high enough to warm the X-ray region that McCammon is investigating.

The other possible source is “Type II” supernovae. The stars behind Type II supernovae are even more massive, burn brighter and hotter, and live only a few million years before becoming supernovae. They occur in active star-forming regions, such as those in one of the inner spiral arms of our galaxy.

To distinguish these possibilities, XQC will analyze the X-ray light, looking for traces of oxygen and iron. More oxygen indicates Type II supernovas, while less oxygen indicates Type Ia supernovas. The physics behind it is complex, but ultimately stems from how long the stars burned before they erupt. The smaller stars behind Type Ia supernovae burn longer and leave behind less oxygen than Type II supernovae.

Of course, the flight will probably also capture a lot more information. “This is an exploration with a new possibility — we want to see what we can see,” McCammon said. “Every time we look at the X-ray sky with a new possibility, it turns out to be more complicated than we thought.”

After the flight, the team plans to recover the instrument. It will retire to Oak Ridge National Labs in Tennessee, where it will aid in lab experiments.

This flight will be XQC’s last trip to space, but the very first of the new Arnhem Space Center rocket series in East Arnhem, Australia. XQC is part of a three-missile campaign to launch from range in June and July 2022, the first time NASA has launched from Australia since 1995.

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Quote: NASA rocket mission probe seeks source of X-rays from inner galaxy (2022, June 21) retrieved June 21, 2022 from rays.html

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