Tools of the astrophysical trade, old and new

by Adam Hadhazy

New telescopes and instruments are always needed to further advance the science of astrophysics, but there are some oldies-but-goodies that continue to deliver

A picture snapped by a Servicing Mission 4 crew member just after the Space Shuttle Atlantis captured the Hubble Space Telescope with its robotic arm on May 13, 2009, beginning the mission to upgrade and repair the telescope. CREDITS: NASA and ESA

The Author

Adam Hadhazy

There's the saying that workers are only as good as their tools, and in observational astrophysics, there is some truth to that statement. Successive generations of telescopes and instruments have gotten often bigger (certainly in the case of telescope mirrors) and always better in terms of precision. Capability has also dramatically expanded from the first optical light telescopes to modern instruments capable of seeing the universe in everything from radio waves to gamma rays, and with increasingly esoteric portions of the electromagnetic spectrum—such as submillimeter light and "hard" x-rays, just to name a couple—increasingly getting their due. But some old tools can still do a job remarkably well, rather like an old hammer that still pounds in nails with the best of them. One such old hammer in astronomers' collective toolkit is the Hubble Space Telescope. Good ol' HST recently celebrated its 31st birthday, having launched in April 1990. It's still cranking out science, both with new observations and from astronomers poring over its vast and still-growing catalog of observations. Without question, HST ranks among the top astrophysical tools ever wielded. It's too soon to say what the legacy will be of a tool celebrating its zeroth birthday, namely the Dark Energy Spectroscopic Instrument (DESI), with which Kavli Institute-affiliated astrophysicists and colleagues have started a five-year observing campaign just this past month. It could be that DESI gathers the data that really unlocks what exactly dark energy is—the literally biggest (seeing as it is theorized to comprise 70% of the universe's mass-energy) mystery in existence. Given all we still don't know about how the universe works, many more innovative tools like DESI will need to be brought to bear. We should also give thanks to the tried-and-true tools, like Hubble, that have helped build the edifice of modern astrophysics.

Catching planet formation in the act

In the PDS 70 solar system, a giant planet is taking shape right before our very eyes, via the Hubble Space telescope. Researchers at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University carefully processed Hubble images to remove the glare of the system's star in order to directly image a fledgling gas giant world. The planet is actively swelling in size, accumulating material that is leftover around the star from the star's recent formation. Hubble's ultraviolet vision even captured the signature of hot gas falling onto the planet—a granular level of planet-making detail that researchers are keen to gather more of in fully fleshing out planet formation models.

Dark matter could reveal itself by overheating exoplanets

Scientists have searched high and low for dark matter. They've sought signatures of the mysterious substance influencing vast gobs of matter at grand cosmic scales and for how it might interact with itself and spew anomalous gamma rays. Scientists have meanwhile kept patient watch for individual, infinitesimal particles of dark matter that might deign to interact with everyday atoms here on Earth. So far, detection-wise, it's been zip, zero. Now a researcher—Rebecca Leane, at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University—is proposing to look for dark matter in a new way, via exoplanets. Specifically, Leane and a colleague have proposed that planets around stars located in the crowded center of our galaxy—where we expect dark matter concentration to be the highest—might accumulate a lot of the stuff over time in their interiors. Those extra-concentrated dark matter particles might self-annihilate and make a planet much hotter than would be expected, based on the planet's other observable properties. The James Webb Space Telescope might be able to detect this telltale heat signature, opening our eyes at last to dark matter.

Regardless of their size, black holes devour matter the same way

Out in the universe, black holes come in a vast range of sizes and masses. So-called stellar mass black holes pack in a few times the mass of the sun into a region perhaps just a few miles wide. Supermassive black holes on the other hand, as their name suggests, can contain billions of times the sun's mass in an approximately solar system-sized expanse. Despite these disparities, it seems that all black holes pull in material in much the same way, according to a new study by members of the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research (MKI). While observing "tidal disruption events"—when stars stray too close to black holes and are gravitationally ripped to shreds—caused by stellar mass and supermassive black holes, the researchers saw the same sequence of events. Flares of light go out from the area of space near the black hole where matter getting pulled in is hyper-accelerated, with some of the matter then settling into an accretion disk. As the matter influx slows, the light signature changes, until the matter is all gone and the black hole returns to a quiescent stage. Indeed, "size matters not," as Yoda might say, when it comes to black holes.

Ready, set, go for the Dark Energy Spectroscopic Instrument

It’s go time! On May 17, researchers officially kicked off the Dark Energy Spectroscopic Instrument's (DESI) five-year observing campaign to create the largest 3D map of galaxies ever assembled. Multiple members of the Kavli Institute for Cosmological Physics (KICP) at the University of Chicago and KIPAC are part of the international DESI collaboration. DESI's claim to fame is that it will gather light signatures, or spectra, from tens of millions of galaxies, or about 10 times as many galaxy spectra as have ever been obtained. Spectra are extremely scientifically valuable because they reveal a galaxy's distance from us, thus enabling DESI to make that 3D map. That map, in turn, will show how dark energy—a poorly understood repulsive force that is accelerating the universe' expansion—has manifested over the eons in driving galaxies apart. DESI will also be quite handy for a wealth of other astrophysical and cosmological investigations, from galaxy evolution to structure formation.

A small section of the DESI focal plane, showing the one-of-a-kind robotic positioners. The optical fibers, which are installed in the robotic positioners, are backlit with blue light in this image. Photo: DESI collaboration

Getting under the skin of massive stars to gauge their elemental mixing

By studying the brightness oscillations of a set of large stars, astronomers have shown that the heretofore hidden mixing of chemical elements inside such stars is wildly diverse. The findings come from a team of researchers led by May Gade Pedersen, a postdoctoral scholar at the Kavli Institute for Theoretical Physics (KITP) at the University of California, Santa Barbara. In their cores, massive stars burn through their hydrogen fuel quickly. The convective roiling within the stars, though, cycles in fresh hydrogen, prolonging the stars' lives before they eventually explode as supernovae. Scientists have long sought insight into this elemental mixing in order to hone stellar evolution models. The technique of asteroseismology, wherein a star's natural fluctuations can be leveraged to reveal internal structure and composition, offered that way in, courtesy of observations gathered by the Kepler space telescope. A successor to Kepler, the Transiting Exoplanet Survey Satellite (TESS), spearheaded by MKI, will gather even more such useful data, helping astronomers further understand the furtive mixing inside stars.

A simulation of a 3-solar-mass star shows the central, convective core and the waves it generates in the rest of the star’s interior. Photo Credit: PHILIPP EDELMANN
Written by Adam Hadhazy

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