‘Lensed’ supernova could shed light on fundamental forces shaping the universe – Ars Technica

Zoom in / Gravitational lensing has revealed a previously unknown supernova explosion more than 4 billion light-years away.

Joel Johansson, Stockholm University

Astronomers detected a previously unknown supernova explosion more than 4 billion light-years away using a rare phenomenon called “gravitational lensing,” which acts as a kind of cosmic magnifying glass. They describe their discovery and its potential implications in a new paper published in the journal Nature Astronomy. Ariel Jobar Co-Author, Director Oscar Klein Center at Stockholm University, described The discovery as “an important step forward in our quest to understand the fundamental forces that shape our universe.”

Gravitational lensing is a direct consequence of general relativity: the collective bends and warps space-time, and light must follow this bending. This phenomenon can form rare effects such as “Einstein’s ring“or”Einstein cross. Essentially, the distortion in space-time caused by a massive object (such as a galaxy) acts as a lens to magnify a background object. Since these are not lenses of perfect optical quality, there is often some distortion and unevenness. This causes the light from the background object to take different paths. to Earth, and thus a single object can appear in several different locations distributed around the lens.On cosmic scales, these paths can also require light to travel very different distances to reach Earth.

Gravitational lensing helps astronomers spot celestial bodies that may be too faint or out of sight, such as a distant supernova, which can lead to other interesting questions. For example, last year, astronomers analyzed a Hubble image from 2010, where the image happened to capture a supernova. Because of gravitational lensing, the individual event appeared in three different locations within Hubble’s field of view. Thanks to quirks of how the lens works, and because light travels at a finite speed, all three locations were shot differently times After the star exploded, allowing researchers for a piece together The time track that followed the supernova, although it was observed more than a decade ago.

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This latest paper focuses on a newly discovered supernova named SN Zwicky, discovered in Zwicky Transit Facility (ZTF). The ZTF is a robotic camera attached to the 70-year-old Samuel Oschin Telescope at Palomar Observatory in San Diego County. The ZTF conducts automated surveys of the night sky, looking for objects that explode or vary in brightness: supernovae, stars that get hit by black holes, asteroids and comets, for example. It scans the entire sky over three nights and the visible plane of the galaxy twice each night.

Astronomers quickly marked the object as interesting because it was unusually bright. They then relied on the adaptive optics tools at three other telescopes—the W.M. Keck Observatory, the Very Large Telescope, and the Hubble Space Telescope—to show four images of the object from different locations in the sky. This confirmed that the supernova’s unusual brightness was a product of gravitational lensing.

Schematic diagram of the strong gravitational lens. Source: ESA/Hubble, L. Calçada.

“SN Zwicky is not only magnified by gravitational lensing, but it also belongs to a class of supernovae that we call ‘standard candles’ because we can use their well-known luminosity to determine distance in space,” said co-author Igor AndreoniHe is a postdoctoral researcher at the University of Maryland and NASA’s Goddard Space Flight Center. “When the light source is far away, the light is dim — just like seeing candles in a dark room. We can compare two light sources in this way and get an independent measure of distance without having to actually study the galaxy itself.”

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SN Zwicky and similar supernovae could one day help scientists resolve the ongoing controversies about Hubble constantIt is a measure of how fast the universe is expanding. As mentioned earlier, we measured it using information in the cosmic microwave background and got a single value. We measured it using the apparent distance of objects in the current universe and got a value that differed by about 10 percent. As far as anyone can tell, there is nothing wrong with any of the measurements, and there is no obvious way to get them to agree. However, just last month, researchers were able to make a third independent measurement of the expansion of the universe by tracking the behavior of a gravitationally lensed supernova identified in 2014 and Now called SN Refsdalafter the astronomer who first proposed using lenticular explosions to make measurements.

When it was first discovered, the lens had made four images of the supernova. But later, a fifth appeared, and this time delay was affected by the expansion of the universe – hence the Hubble constant. The best fit for the new models all ended up being slightly less than the value of the Hubble constant derived from the cosmic microwave background, with the difference being within the statistical error. Values ​​closer to those derived from measurements of other supernovae were a better fit to the data, though the team was careful to say that didn’t mean we should rule out a higher value.

Lensing supernovae can also be promising tools for investigating dark energy and dark matter. Case in point: In April, the researchers argued that There are features in gravitational lensing that may be better explained by axon-like properties, in contrast to the long-favorite and still elusive WIMPs (Weakly Interacting Massive Particles). Axions are much lighter than WIMPs but have other properties consistent with dark matter. The April analysis likely makes axions much lighter than neutrinos. (It is worth noting that the authors have expressed caution about the evidence for their hypothesis so far.)

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In short, “This discovery paves the way for finding more of these rare lenticular supernovae in future large surveys that will help us study transient astronomical events such as supernovae and gamma-ray bursts,” Andreone said. “We look forward to more unexpected discoveries using nontarget wide-sky surveys like the one that helped us identify SN Zwicky.”

DOI: Nature Astronomy, 2023. 10.1038 / s41550-023-01981-3 (about DOIs).

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