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08/13/2020 - From Quanta to Galaxies: Astrophysics Highlights

By Adam Hadhazy

scientist works on LIGO machinery in a protective suitMIT physicists have observed that LIGO’s 40-kilogram mirrors can move in response to tiny quantum effects. In this photo, a LIGO optics technician inspects one of LIGO’s mirrors. Credit: Matt Heintze/Caltech/MIT/LIGO Lab

​​Astrophysics and its related fields are the sciences of the biggest objects in existence. These objects range from planets to stars, on up to great assemblages of stars and other material into galaxies, and then galaxies into colossal clusters and filaments, and finally the whole of the universe and existence. Heady stuff. So much so that one might think that the infinitesimal goings-on of the particles that compose reality on the smallest of scales would be, well, like climatologists concerning themselves with ants. (Though of course that analogy fails to capture the true disparateness of the scales involved.) Yet the successful pursuit of understanding the universe at its absolute biggest is thoroughly intertwined with understanding of it at its absolute smallest; the parts do, across magnitudes upon magnitudes, make up the whole. This concern for the smallest scales also extends to the experimental apparatuses that astrophysicists and engineers devise to measure cosmic phenomena. As you'll read on to find out, detecting the tiniest quantum jiggle felt within a vast machine can be key for honing our abilities to study the universe at large.

  • Fluctuations on the tiniest quantum scales can move big objects

In order to register the infinitesimal perturbations of gravitational waves passing through Earth, LIGO—the Laser Interferometer Gravitational-wave Observatory—was designed to detect displacements of laser beams as small as ten-thousandths of the diameter of a proton. Part of this incredible sensitivity is factoring in "quantum noise," created by so-called virtual particles that flit in and out of existence at Lilliputian scales. Now researchers working on LIGO from the Massachusetts Institute of Technology's Kavli Institute for Astrophysics and Space Research (MKI) have, for the first time, detected this quantum noise moving a truly macroscale object. That object is a 40-kilogram mirror in LIGO, which is a billion times heavier than the objects where the quantum effect has been previously detected. The quantum jiggle is tiny—just 10-20 meters, or the size of a proton to a proton, and only detectable because the mirror is so highly stabilized compared to an everyday object. Nevertheless, it is a remarkable demonstration of the weird-but-true nature of quantum mechanics, and points to how LIGO can be sensitized even further to grav waves.

  • A quantum noise-cancelling device for even more precise experiments

Speaking of quantum noise, MKI researchers also announced the development of a new "quantum squeezer" device that cuts the pesky noise in incoming laser beams by 15%. What's more, the system is the first of its kind to function at room temperature. That means the device can be compact and portable, thus easing incorporation into hyper-sensitive experiments to boost their precision. Made of a mirror and a cantilever, the device is designed to absorb a minimal amount of thermal energy from a laser, which translates into less jittery, quantum-noise-induced movement. Applications include better quantum computers and enhanced gravitational wave detection by experiments such as LIGO.

  • Nailing down the expansion rate of the universe is like nailing Jell-O to the wall

One of the biggest mysteries in current cosmology is the true speed at which the universe is expanding, a figure known as the Hubble constant. The conflict arises between measurements of the local universe's expansion versus the expansion predicted by studies of the universe's beginnings nearly 14 billion years ago. The latest entrant in this debate is a 3D map that spans a good deal of the middle ground between these viewpoints, covering 11 billion years of cosmic history. This map agrees with the rate of the early universe, contrasting with the modern universe measurements; in short, the plot has thickened. Wendy Freedman, a member of the Kavli Institute for Cosmological Physics (KICP) at the University of Chicago, a leader of the modern universe measurements, spoke to New Scientist and commented on the possibility that some key physics are likely missing still, and will be needed to solve this conundrum.

  • Universe's age is further solidified as being right around a ripe old 13.8 billion years

Researchers have taken a fresh look at the cosmic microwave background, which is the oldest light in the universe, with the Atacama Cosmology Telescope (ACT) in Chile. The telescope's observations of this "afterglow" of the Big Bang estimate the universe's age as 13.77 billion years, in remarkable agreement with prior, high-precision measurements and aligning with the prevailing cosmological model. Dating the universe is linked to knowing its expansion rate (just mentioned above), so these new results are one more piece of evidence to consider. David Spergel of the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) at the University of Tokyo was involved in the findings.

  • Black hole's corona pulls off a temporary disappearing act

Black holes are famous for being lightlessly invisible. But the hyper-dense objects do give themselves away when their intense gravity accelerates and collides matter surrounding them. Now in a first, MKI researchers have observed the light outpouring from a black hole's surrounding, billion-degree ring—called a corona—suddenly vanish. The thinking is that a star wandered too close and disrupted the ring, causing its constituent particles to actually fall into the black hole. After a few months, the black hole reformed a corona as it dragged fresh particles into its gravitational clutches. What's for sure is that black hole behavior continues to offer surprises.

artist's illustration of a black holeImage credit: NASA/JPL-Caltech

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