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Today’s astronomers are much better prepared for the next supernova than Kepler would have been—or than anyone would have been just a few decades ago. Today’s scientists are equipped with telescopes that record visible light. These instruments will show what a supernova would look like if we could fly close to it and look at it with our own eyes. But we also have telescopes that can record infrared light—light whose colors lie beyond the red end of the visible spectrum. With its longer wavelengths, infrared light can pass more easily through gas and dust than visible light, revealing targets that may be impossible to see with traditional telescopes. The James Webb Space Telescope, for example, records primarily in the infrared. Both visible and infrared light are part of the “electromagnetic spectrum,” but supernovas also emit a different kind of radiation, in the form of subatomic particles called neutrinos—and today we have detectors to snare them, too. As well, astronomers now have detectors that can record subtle ripples in the fabric of spacetime known as gravitational waves, which are also believed to be unleashed by exploding stars. A supernovaonly burns for a small while, yeteach one lets out an incredible amount of information regarding our universe. The first type of supernova is associated with binary star systems. Binary stars are two stars that orbit the same point, or center of mass. When one of the stars—a white dwarf(a highly dense star not much bigger than our sun)—steals matter from its companion star as it orbits the axis, it begins to accumulate enormous amounts of matter. This causes the star to eventually explode, resulting in a supernova. Supernova of a binary star(Photo Credit: Wikimedia Commons) Stars with initial masses less than about 8 M ☉ never develop a core large enough to collapse and they eventually lose their atmospheres to become white dwarfs. Stars with at least 9 M ☉ (possibly as much as 12 M ☉ [114]) evolve in a complex fashion, progressively burning heavier elements at hotter temperatures in their cores. [108] [115] The star becomes layered like an onion, with the burning of more easily fused elements occurring in larger shells. [100] [116] Although popularly described as an onion with an iron core, the least massive supernova progenitors only have oxygen- neon(- magnesium) cores. These super-AGB stars may form the majority of core collapse supernovae, although less luminous and so less commonly observed than those from more massive progenitors. [114]

An illustration of the night sky showing the location of galaxy M101 near Ursa Major (UMa) and Boötes (Boo). (Image credit: TheSkyLive.com)In 2022 a team of astronomers led by researchers from the Weizmann Institute of Science reported the first supernova explosion showing direct evidence for a Wolf-Rayet progenitor star. SN 2019hgp was a type Icn supernova and is also the first in which the element neon has been detected. [133] [134] Electron-capture supernovae [ edit ] A few percent of the type Ic supernovae are associated with gamma-ray bursts (GRB), though it is also believed that any hydrogen-stripped type Ib or Ic supernova could produce a GRB, depending on the circumstances of the geometry. [125] The mechanism for producing this type of GRB is the jets produced by the magnetic field of the rapidly spinning magnetar formed at the collapsing core of the star. The jets would also transfer energy into the expanding outer shell, producing a super-luminous supernova. [112] [126] [127] It is now known by direct observation that much of the light curve (the graph of luminosity as a function of time) after the occurrence of a type II Supernova, such as SN 1987A, is explained by those predicted radioactive decays. [8] Although the luminous emission consists of optical photons, it is the radioactive power absorbed by the ejected gases that keeps the remnant hot enough to radiate light. The radioactive decay of 56Ni through its daughters 56Co to 56Fe produces gamma-ray photons, primarily with energies of 847 keV and 1,238keV, that are absorbed and dominate the heating and thus the luminosity of the ejecta at intermediate times (several weeks) to late times (several months). [147] Energy for the peak of the light curve of SN1987A was provided by the decay of 56Ni to 56Co (half-life 6 days) while energy for the later light curve in particular fit very closely with the 77.3-day half-life of 56Co decaying to 56Fe. Later measurements by space gamma-ray telescopes of the small fraction of the 56Co and 57Co gamma rays that escaped the SN 1987A remnant without absorption confirmed earlier predictions that those two radioactive nuclei were the power sources. [146] Messier 61 with supernova SN2020jfo, taken by an amateur astronomer in 2020

Scientists have described two distinct types of supernovas. In a Type I supernova, a white dwarf star pulls material off a companion star until a runaway nuclear reaction ignites; the white dwarf is blown apart, sending debris hurtling through space. Kepler’s was a Type I. In a Type II supernova, sometimes called a core-collapse supernova, a star exhausts its nuclear fuel supply and collapses under its own gravity; the collapse then “bounces,” triggering an explosion.Calcium-rich supernovae are a rare type of very fast supernova with unusually strong calcium lines in their spectra. [65] [66] Models suggest they occur when material is accreted from a helium-rich companion rather than a hydrogen-rich star. Because of helium lines in their spectra, they can resemble type Ib supernovae, but are thought to have very different progenitors. [67] Type II [ edit ] Light curves are used to classify type II-P and type II-L supernovae. [61] [68]

About 10 million years ago, a cluster of supernovas created the "Local Bubble," a 300-light-year-long, peanut-shaped bubble of gas in the interstellar medium that surrounds our solar system. Astronomers will certainly continue to monitor the supernova in the days to come, noting any fluctuations in brightness before it eventually fades away.

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Supernovae have shown scientists that we live in an expanding universe (by observing the redshift), one that is growing at an ever-increasing rate. Astronomers have concluded that supernovae play a vital role in distributing the elements produced in their cores throughout the universe. Could a nearby supernova pose a threat to life on Earth? Yes, in theory—but the blast would have to be very close, and at the moment no such nearby stars are at risk of exploding. Which is a good thing, because the blast of radiation from a nearby supernova would be devastating. Over a period of weeks, the supernova would emit ultraviolet rays, X-rays and gamma rays, which wouldn’t necessarily reach the ground, but would still wreak havoc on the Earth’s protective ozone layer, explains Fields. “So it wouldn’t turn us into the Hulk—but it would strip the ozone layer off the stratosphere,” he says. Without the ozone layer, the Earth would be awash in deadly ultraviolet radiation from the sun; this could wipe out phytoplankton in the oceans, with the effects working their way up the food chain, possibly leading to a mass extinction, Fields says. There is no formal sub-classification for non-standard type Ia supernovae. It has been proposed that a group of sub-luminous supernovae that occur when helium accretes onto a white dwarf should be classified as type Iax. [94] [95] This type of supernova may not always completely destroy the white dwarf progenitor and could leave behind a zombie star. [96] So the resultant light from this explosion has been traveling through space for 21 million years before it finally reached our planet last week. Core collapse can be caused by several different mechanisms: exceeding the Chandrasekhar limit; electron capture; pair-instability; or photodisintegration. [100] [101] [102]

That’s what the German astronomer Johannes Kepler saw in 1604; skywatchers elsewhere in Europe, the Middle East and Asia saw it too. We now know it wasn’t really a new star but rather a supernova explosion—an enormous blast that happens when certain stars reach the ends of their lives. Either type of supernova can be so bright as to briefly outshine an entire galaxy. But Type II supernovas are particularly interesting because they release not only light but also enormous numbers of neutrinos. In fact, the emission of neutrinos can start a little bit ahead of the explosion itself, explains Kate Scholberg, an astronomer at Duke University. NASA, 2013. "What Is a Supernova?" https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-supernova.html With that observation, they became the first astronomers to catch a star in the act of exploding. The new supernova was named SN 2008D. Further study has shown that the supernova had some unusual properties.

The life cycle of a star leading to a supernova

Eventually, the core gets immensely dense, to the point where it can no longer withstand its own gravitational force. This results in a core collapse, paving the way for a catastrophic and violent explosion, known as a supernova.Think about how massive our sun is, in comparison to its planets, and yet its mass is nowhere near a supermassive star that could end in a supernova. A few supernovae, such as SN 1987K [69] and SN 1993J, appear to change types: they show lines of hydrogen at early times, but, over a period of weeks to months, become dominated by lines of helium. The term "type IIb" is used to describe the combination of features normally associated with types II and Ib. [61] Next, gradually heavier elements build up at the center, and the star forms onion-like layers of material, with elements becoming lighter toward the outside of the star. Once the star's core surpasses a certain mass (called the Chandrasekhar limit), it begins to implode. For this reason, these Type-II supernovae are also known as core-collapse supernovae. The model for the formation of this category of supernova is a close binary star system. The larger of the two stars is the first to evolve off the main sequence, and it expands to form a red giant. The two stars now share a common envelope, causing their mutual orbit to shrink. The giant star then sheds most of its envelope, losing mass until it can no longer continue nuclear fusion. At this point, it becomes a white dwarf star, composed primarily of carbon and oxygen. [84] Eventually, the secondary star also evolves off the main sequence to form a red giant. Matter from the giant is accreted by the white dwarf, causing the latter to increase in mass. The exact details of initiation and of the heavy elements produced in the catastrophic event remain unclear. [85]