Editor’s note: A version of this was previously published on the author’s website.
Exploration has entered a new golden age akin to the age of sail during the Renaissance. Instead of seafarers heading west in galleons seeking gold and conquest, astronomers in labs and observatories are discovering realms of astonishing power and beauty high above our heads, including icy moons and exploding supernovas, pulsing dead stars, exoplanets and white-hot vortexes whirling around black holes.
Daniel R. Wik, assistant professor of physics and astronomy at the University of Utah, is among the scientists unraveling these mysteries. He and colleagues in the field of X-ray astronomy research the depths of space, mapping locations and deducing characteristics of black holes, neutron stars and other exotic objects by studying their high-energy X-rays.
Recently Wik addressed the Utah Astronomy Club about X-ray technology, strange astronomical objects and his role in the exploration. The club meets the second Wednesday of the month in the University of Utah’s North Physics Building. The sessions’ host is Paul Ricketts, director of the U.’s South Physics Observatory.
Using data drawn mostly from NASA’s Nuclear Spectroscope Telescope Array (NuSTAR), an orbiting X-ray telescope, Wik studies galaxies and galaxy clusters. The instrument is an advance because it’s the first to focus high-energy X-rays to show relatively clear detail. It has examined sources of X-rays in the Whirlpool Galaxy, a group of supermassive black holes, Andromeda, the sun and other objects.
Previously an English teacher in China and a researcher at the Goddard Space Flight Center in Greenbelt, Maryland, Wik also analyzes data from other satellite X-ray observatories, including NASA’s Chandra and the European Space Agency’s X-ray Multi-Mirror Mission. He joined the University of Utah in August 2017.
Earlier observatories were limited to recording lower-energy X-rays, a range that is “sort of restricted,” Wik said, because high-energy radiation passes through lenses or ordinary mirrors without much deflection; high-energy photons can’t be focused by the earlier satellites. NuSTAR uses a set of 133 glass “shells” glued together to gently bend the photons so that they come to a focus.
- NuSTAR’s two optical devices each include 133 layers of glass, coated with refractive compounds, stacked together in a cylinder. The layers allow X-rays to be gently bent into a focused beam. On the left is a side view showing how the layers are stacked; on the right, an overall view. NASA/Jet Propulsion Laboratory-California Institute of Technology, Pasadena
- An illustration shows how a cylinder of curved mirrors can focus X-rays. Each of the NuSTAR collectors has 133 layers of mirrors. Illustration provided by Goddard Space Flight Center/NASA
The satellite’s two telescopic collectors, nestled glass contraptions, are aimed at the detector at the end of a boom 33 feet long.
”There weren’t telescopes before NuSTAR to go to these high energies,” Wik told a rapt audience of more than two dozen.
The glass shells were made in segments. Glass was melted in molds called mandrels, which cast each in the right size and shape. Then the thousands of mirror segments needed to be coated with material that would gently bend the X-rays. “That coating was done in Denmark,” he said. “All of this glass had to be shipped to Denmark.”
NuSTAR was an inexpensive project for its type, and the budget wasn’t big enough to cover insuring the segments. “So then they just shipped it uninsured and hoped for the best,” he said.
In Denmark, a machine coated the glass with atomized material — many alternating layers of a platinum compound and a compound including tungsten. The coated segments were shipped back to Columbia University in New York City for assembly. “They had to glue all this glass together.” Segments were glued atop one another with spacers about 4/100 of an inch thick.
In 2010, after earning his doctorate in astronomy from the University of Virginia, Charlottesville, Wik began working at Goddard, helping to calibrate NuSTAR’s mirrors. He described difficult working conditions, such as having to go outside at night in February to turn the X-ray machine on and off when it malfunctioned. The machine was about 525 feet away, requiring a “perilous trek” through trees that would nearly snag him every time.
To align the optics, which cost about $50 million apiece, scientists had to block part of the mirrors with a 50-pound lead plate, which was maneuvered between the mirrors and a camera that cost $20,000 or $30,000. Camera and optics were about a foot apart with the heavy sheet between. It was “very important never to touch” the equipment. Since the operation was done inexpensively, the lead plate was suspended from cheap plastic rollers by bungee cords. The rollers would stick as they moved the plate and they would have to jostle it to get it going. Then it would swing on the cords “and you’d just have to try to keep it from hitting anything.”
NuSTAR was lifted to orbit on June 13, 2012. It was loaded aboard a Pegasus rocket, and the rocket was hung below a Stargazer L-1011 aircraft. The rocket dropped from the Stargazer and it fired into low-Earth orbit. The launch was from the Ronald Reagan Ballistic Missile Defense Test Site on Kwajalein Atoll, Marshall Islands. This drew an involuntary yell from the blog’s author, who grew up on Kwajalein Island in the 1960s.
Once in orbit, the boom slowly extended and locked into place.
NuSTAR has been making observations ever since and is still working well, Wik noted.
A singular triumph was its observations of the Andromeda Galaxy 2.5 million light-years distant, the closest large spiral galaxy to the Milky Way. Over nine months, during which exposures totaled about a month, NuSTAR built up an unprecedented look at high-energy X-ray sources there. Wik showed a photo of Andromeda taken in ultraviolet light overlain by the four adjacent plats where NuSTAR made its readings. High-energy X-ray sources show up in about 60 areas, he said.
The telescope detects hard radiation from X-ray binary sources and other objects like supernovas and supermassive black holes. Binary sources are expanding, dying stars in orbit with a compact object, either a neutron star or a black hole. Hot gas from the dying star is stolen by the gravity of the companion, forming a disk around the black hole or neutron star, he said.
Supermassive black holes are believed to exist at the center of almost all galaxies. But NuSTAR did not see one in the Andromeda nucleus. The reason probably is that the black hole is inactive just now, not pulling in copious amounts of material and thus not emitting much radiation.
Utah Astronomy Club member Dave Bernson, one of the state’s most knowledgeable amateur star-gazers, remarked, “Monsters only scream when they eat.” Wik agreed, saying our galaxy’s supermassive black hole happens to be fairly quiet presently too. However, he said, one of NuSTAR’s first observations was of a flare that erupted when it encountered something, probably a gas cloud.
”There are lots of sources” of hard X-rays in the Andromeda view, he said, but none where the supermassive black hole is thought to lurk. One source that shows that type of radiation was thought to be a black hole within Andromeda about 10 times the mass of the sun. It is the light bluish blob in the left field of view, well within M31’s disk. But analysis shows that instead, the black hole is probably a million times the mass of the sun.
The source is “in a galaxy that’s many, many light-years beyond this galaxy,” Wik said. “So it’s just shining through M31.”
Joe Bauman, a former Deseret News science reporter, writes an astronomy blog at the-nightly-news.com and is an avid amateur astronomer. His email is firstname.lastname@example.org.