NASA Sounding Rocket Mission Seeks Source of X-rays Emanating From Inner Galaxy

This post was originally published by NASA

To human eyes, the night sky between the stars appears dark, the void of space. But X-ray telescopes capture a profoundly different view. Like a distant firework show, our images of the X-ray sky reveal a universe blooming with activity. They hint at yet unknown cosmic eruptions coming from somewhere deeper into 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 observe a patch of X-ray light with 50 times better energy resolution than ever before, key to revealing its source. The launch window opens at Equatorial Launch Australia’s Arnhem Space Centre in Northern Territory, Australia, on June 26, 2022.

Because Earth’s atmosphere absorbs X-rays, our first views of cosmic X-rays awaited 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 spread across the sky. The discovery founded the field of X-ray astronomy and later won Giacconi a share of the 2002 Nobel Prize in physics.

a heatmap of the night sky that is mostly blue but has a few blobs of green and warmer colors like orange and red. One of the blobs is circled, indicating the area that McCammon's team is focusing on
This image shows a “map” of the night sky in soft X-ray light in galactic coordinates, with the Sun positioned at the center. The horizontal line across the middle of the image runs along the plane of our disk-shaped galaxy. University of Wisconsin, Madison astronomer Dan McCammon and the XQC team will be observing 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, cut in half by cold absorbing gas in the plane of the galaxy.
Credits: Snowden et al., 1997

Scientists have now mapped the X-ray sky in ever-finer detail with the help of other NASA X-ray missions. Still, there are several bright patches whose sources are unknown. For the upcoming flight, McCammon and his team will target a patch of X-ray light only partly visible from the Northern Hemisphere.

“It covers a big part of the galaxy, but we needed 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 patch comes from diffuse, hot gas heated by supernovae, the brilliant eruptions of dying stars. The XQC mission is investigating two possible sources, illustrated in the graphic below.

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

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

To distinguish these possibilities, XQC will analyze the X-ray light, looking for traces of oxygen and iron. More oxygen points to Type II supernovae, while less oxygen suggests Type 1a supernovae. The physics behind it is complex but ultimately stems from how long the stars burned before erupting. The smaller stars behind Type 1a supernovae burn for longer, leaving less oxygen behind than Type II supernovae.

Of course, the flight is likely to capture much more information as well. “This is an exploration with a new capability – we want to see what we can see,” McCammon said. “Every time we look at the X-ray sky with a new capability, it turns out to be more complicated that we supposed.”

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 laboratory experiments.

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

Sau Lan Wu honored with named planet

The International Astronomical Union (IAU) has named a minor planet ‘Saulanwu’ after UW–Madison physics professor Sau Lan Wu.

The planet (177770) ‘Saulanwu’ (=2005 JE163) was discovered on May 8, 2005 at Mt Lemmon observatory in southern Arizona by a NASA funded project, the Catalina Sky Survey. More details about the planet can be found from NASA’s JPL website, including a sketch of the planet’s orbit, which is in the asteroid belt between Mars and Jupiter. Minor planet ‘Saulanwu’ is about two kilometers in diameter, and it takes four years to orbit the sun once. This planet is relatively stable, dynamically, and is expected to remain in our cosmos for millions of years to come.

Wu was nominated for this honor by astronomer Gregory J. Leonard from the University of Arizona’s Department of Planetary Sciences.

a certificate announcing that Sau Lan Wu has had a minor planet named after her

Victor Brar, Moritz Münchmeyer funded through latest round of Research Forward

Victor Brar

Sixteen projects — including two from Physics — have been selected for funding in the second round of Research Forward, a program to stimulate innovative and groundbreaking research at UW–Madison that is collaborative, multidisciplinary and potentially transformative.

The winning projects were chosen from 96 proposals submitted by applicants across campus. The Research Forward initiative is sponsored by the Office of the Vice Chancellor for Research and Graduate Education and is supported by the Wisconsin Alumni Research Foundation, which provides funding for one or two years, depending on the needs and scope of the project. Some of the projects that have been funded have the potential to fundamentally transform a field of study.

profile photo of Moritz Muenchmeyer
Moritz Münchmeyer

The Research Forward initiative is sponsored by the Office of the Vice Chancellor for Research and Graduate Education and is supported by the Wisconsin Alumni Research Foundation, which provides funding for one or two years, depending on the needs and scope of the project. Some of the projects that have been funded have the potential to fundamentally transform a field of study.

“Research Forward encourages collaboration among campus PIs, enhances PhD student and postdoc training, and strengthens our external grant funding requests,” says Steve Ackerman, vice chancellor for research and graduate education. “The projects we selected are truly forward-looking and use innovative approaches and tools such as state-of-the-art machine learning methods, 3D printing techniques and geostationary satellites.”

The Physics projects are:

Keith Bechtol selected to Department of Energy Early Career Research Program

profile photo of keith bechtol
Keith Bechtol

The Department of Energy’s (DOE) Office of Science announced the selection of 83 scientists — including University of Wisconsin–Madison physics professor Keith Bechtol — to the Early Career Research Program.

The funding will allow Bechtol and his group to first work on commissioning the Vera C. Rubin Observatory in preparation for the Legacy Survey of Space and Time (LSST), then they will transition to data collection and analysis for their cosmology research.

“We are anticipating that LSST will catalog more stars, more galaxies and more solar system objects during its first year of operations than all previous telescopes combined,” Bechtol says.

Rubin Observatory’s telescope will have an eight-meter diameter mirror and a ten square degree field of view. The 3.2-billion-pixel camera will collect an image every 30 seconds. All told, LSST will amass around 10 terabytes of data every night.

Bechtol has leadership roles for building and commissioning the observatory as well as with the Dark Energy Science Collaboration (DESC), the international science collaboration that will make high accuracy measurements of fundamental cosmological parameters using LSST data. At least seven other collaborations have formed around different science areas to analyze the data. Rubin Observatory is preparing to serve the LSST data to many thousands of scientists in the US, Chile, and at international partner institutions around the world.

“DESC will use LSST data to address several outstanding physics questions, such as: Why are the distances between galaxies growing at an accelerating rate? What is the fundamental nature of dark matter? What is the absolute mass scale of neutrinos? How did the universe begin and what were the initial conditions?” Bechtol says.

Bechtol will receive around $150,000 per year for five years to cover summer salary and research expenses. The research expenses will be used mostly to cover the analyses after the data collection starts. However, because there cannot be useful data without the initial commissioning and science validation steps — and because the Observatory is still a couple of years away from first light — the DOE award is also supporting Bechtol’s efforts during the commissioning phase to accelerate the realization of DESC science goals.

“For me, the most important thing about this award is that it will provide more opportunity for students and postdocs to directly contribute to this ambitious experiment. Turning on a new experiment of this scale and complexity doesn’t happen every day,” Bechtol says. “For my research group to be able to participate firsthand in the commissioning, seeing first light, and contributing to the first cosmology results is so valuable from a career development perspective. We are training the next generation of experiment builders.”

The DOE early career program is open to untenured, tenure-track professors at a U.S. academic institution (or a full-time employee at a DOE national laboratory) who received a PhD within the past 10 years. Research topics are required to fall within one of the DOE Office of Science’s eight major program offices, including high energy physics, the program through which Bechtol’s award was made.


Thad Walker honored with Vilas Distinguished Achievement Professorship

profile photo of Thad Walker
Thad Walker

Extraordinary members of the University of Wisconsin–Madison faculty, including physics professor Thad Walker, have been honored during the last year with awards supported by the estate of professor, U.S. senator and UW Regent William F. Vilas (1840-1908).

Walker was one of seventeen professors were named to Vilas Distinguished Achievement Professorships, an award recognizing distinguished scholarship as well as standout efforts in teaching and service. The professorship provides five years of flexible funding — two-thirds of which is provided by the Office of the Provost through the generosity of the Vilas trustees and one-third provided by the school or college whose dean nominated the winner.

In addition, nine professors received Vilas Faculty Mid-Career Investigator Awards and six professors received Vilas Faculty Early Career Investigator Awards.

Detailed analysis of old star provides template for heavy element formation

This story was originally published by University Communications

The fusion furnaces that are the universe’s stars create the elements from helium up to iron. But iron is only number 26 on the periodic table out of well over 100 known elements. So the heavier ones, like gold, lead and uranium, must come from somewhere other than fusion.

Scientists have long known that those heavy elements come from neutron capture, where neutrons are added to an element that make it unstable, then it radioactively decays and its atomic number increases by one. Nearly 70 years ago, they confirmed one site, or event, of a neutron capture method known as the slow, or s-process. The rapid, or r-process, was not confirmed with a site until 2017, when the LIGO/VIRGO collaboration detected a neutron star merger.

“With a neutron star merger, the neutron stars are ripped apart and they throw out neutrons, and you can build lots of heavy elements out of these neutron stars,” says Jim Lawler, a professor of physics at the University of Wisconsin–Madison. “The mystery arises when we look at the total r-process inventory of our home galaxy: Can we explain all that with neutron star mergers or are there additional sites?”

In a new study led by astronomers from the University of Michigan, Lawler and colleagues identified the elemental composition of HD 222925, a Milky Way star located over 1400 lightyears from earth. Their analysis confirmed that the star was rich in r-process elements, and they were able to identify and calculate the relative abundance of each element. They also found that the star is iron- and metal-poor, a proxy for age that indicates HD 222925 is relatively old and provides information about early star formation.

“We were able to determine a complete r-process abundance pattern for what we think is probably one event that happened early in the beginning of the universe,” Lawler says. “So that r-process template now can be used to screen various models of the nuclear physics that produce the r-process and see if the models for all sites are physically correct.”

At UW–Madison, Lawler and scientist Elizabeth Denhartog contributed the spectroscopic analysis that identified the elements in the star. Every element has a unique electromagnetic spectrum that can be separated into spectral lines using a diffraction grating — just like a prism separates white light into a rainbow. HD 222925 is a relatively bright star, meaning it provided stronger spectra to analyze. It was also identified by the Hubble Space Telescope, providing access to data in the ultraviolet range that is normally blocked by the ozone layer and undetectable by telescopes on Earth.

For the full story, read more on the University of Michigan’s news site.