AC6C. Stay Current—Dramatic Change in Stars

A Changing Cosmos Cover

Staying current for Chapter 6

{ A Changing Cosmos Contents }

Articles from 2006–present

2024-03-27. Black hole at center of Milky Way may be blasting out a jet. [] By DANIEL CLERY, Science. Excerpt: The supermassive black holes at the centers of many galaxies generate powerful jets, blasting particles thousands of light-years into space. This new image of the Milky Way’s black hole, known as Sagittarius A* (Sgr A*), suggests it may have one, too, but perhaps of a more modest nature. The image—taken with polarized light—was released today by the Event Horizon Telescope (EHT), a worldwide array of radio telescopes that in 2019 produced the first ever image of a black hole. The new image shows light that is oriented in a particular direction, revealing magnetic field lines around the black hole. Although jets would not be visible in such a zoomed-in image, strong magnetic fields are thought to be essential in launching them…. See also European Southern Observatory press release.

2024-02-22. Stellar remains of famed 1987 supernova found at last. [] By DANIEL CLERY, Science. Excerpt: When a nearby star exploded in 1987, it created the first supernova visible to the naked eye in 4 centuries and became one of the most intensely studied objects in space. Now, after more than 35 years of searching, researchers have finally discovered the cinder left behind. Using NASA’s new giant space telescope JWST, astronomers spotted glowing gas at the center of the blast that can only have been energized by something hot and compact inside it, they report this week in Science. They believe a neutron star, all that remains of the shattered star, is responsible….

2023-11-14. Cosmic blast seared Earth’s atmosphere from 2 billion light-years away. [] By DANIEL CLERY, Science. Excerpt: On 9 October 2022, for 7 minutes, high energy photons from a gigantic explosion 1.9 billion light-years away toasted one side of Earth as never before observed. The event, called a gamma ray burst (GRB), was 70 times brighter than the previous record holder. …It also ionized atoms across the ionosphere, which spans from 50 to 1000 kilometers in altitude, researchers say. The findings highlight the faint but real risk of a closer burst destroying Earth’s protective ozone layer…. See also New York Times article A Supernova ‘Destroyed’ Some of Earth’s Ozone for a Few Minutes in 2022.

2023-07-06. The Starwatcher. [] By Dennis Normile. Excerpt: Amateur astronomer Koichi Itagaki is one of the most prolific supernova hunters of all time. …he drove to his private observatory in the hills above his home in Yamagata, Japan, 290 kilometers north of Tokyo. …SN 2023ixf is his 172nd supernova, a total topped only by U.S.-based Tim Puckett, whose private observatory in Georgia has bagged at least 360 supernovae with the help of a worldwide network of volunteers who manually examine his images. Itagaki, by contrast, works alone. He “is one of the most prolific supernova observers in the world,” says Andrew Howell, an astronomer at the University of California (UC), Santa Barbara….

2023-06-28. Long-sought hum of gravitational waves from giant black holes heard for first time. [] By Adam Mann, Science. Excerpt: By turning networks of dead stars into galaxy-size gravitational wave detectors, radio astronomers have tuned into the slowly undulating swells in spacetime thought to arise from pairs of supermassive black holes (SMBHs) that are about to collide. In a simultaneous announcement today, five separate international teams said that after nearly 20 years of effort they had found evidence for these gravitational waves. They are far longer than the waves first captured by ground-based detectors in 2015, which emanate from collisions of star-size objects. The findings not only open up a new window in gravitational wave astronomy, but will also help researchers answer questions about the origin and evolution of SMBHs, objects that sit at the center of galaxies and weigh as much as billions of Suns….

2023-05-28. A Star Blows Up in Nearby Galaxy. [] By Andrew Fraknoi. Excerpt: In a galaxy not so “far, far away,” called the Pinwheel Galaxy (or by its catalog number, M101,) astronomers have seen a star explode. Some 21 million lightyears from us — which, believe it or not, is “close” as far as astronomers are concerned — a massive star ended its life by blowing most of itself into smithereens. We call such an explosion a supernova, a word that has entered popular culture as the name of at least five movies and a jazz album. This supernova was only discovered on May 19th, and is still getting brighter and brighter. Some of these explosions can become so bright that they outshine their entire galaxy. We’ll have to see how bright this one gets. …Our best estimates are that the star that blew up had enough material in it to make 15 of our Suns. …We estimate that one such supernova goes off in a galaxy like our Milky Way once every 50-75 years. But M101 is a bigger galaxy, containing some one trillion, or a thousand billion, stars. (Like the national debt, such numbers are hard to take in.) So M101 is a source of more supernovae. The last one we saw in that galaxy was in 2011, not that long ago. …any gold jewelry you happen to wearing, was made through the death of another massive star, many billions of years ago …and is now on your finger, neck, or wrist. Pretty cool!…

2023-03-19. What Lit the Lamps That Let Humanity Measure the Universe. [] By Ruediger Pakmor. Excerpt: Every year around 1,000 Type Ia supernovas erupt in the sky. These stellar explosions brighten and then fade away in a pattern so repeatable that they’re used as “standard candles”—objects so uniformly bright that astronomers can deduce the distance to one of them by its appearance. Our understanding of the cosmos is based on these standard candles. Consider two of the biggest mysteries in cosmology: What is the expansion rate of the universe? And why is that expansion rate accelerating? Efforts to understand both of these issues rely critically on distance measurements made using Type Ia supernovas. …In 1993, the astronomer Mark Phillips plotted how the luminosity of Type Ia supernovas changes over time. Crucially, nearly all Type Ia supernovas follow this curve, known as the Phillips relationship. This consistency—along with the extreme luminosity of these explosions, which are visible billions of light-years away—makes them the most powerful standard candles that astronomers have. But what’s the reason for their consistency? …published simulations in 2021 that played out the aftermath of a D6 detonation. The radioactive nickel-56 nuclei should disintegrate into additional particles, which will then spend months decaying and interacting in the region around the supernova. (Most of our earthly manganese, nickel and cobalt, and a large fraction of our iron, probably originated in reactions such as these.) …Shen and company simplified the math: They assumed the supernova is perfectly spherical and then simulated the physics along a single line radiating outward from the center. …Strikingly, this “one-dimensional” simulation yielded the correct luminosity curve….

2023-03-07. Watch the Milky Way’s Black Hole Spaghettify a Cloud. [] By Monica Young, Sky & Telescope. Excerpt: If you’ve ever wondered what it’s like to fall into a black hole, a dusty gas cloud in the galactic center can give you an idea. Observations of the cloud dating back to 2002 show it’s coming apart in the presence of the supermassive behemoth residing there. That black hole, called Sgr A*, exerts tidal forces on any objects nearby, pulling harder on the nearer side than on the farther side, and stretching — or spaghettifying — them in the process. The extent of the black hole’s effects depends on the density of the object itself: A cloud will stretch like taffy while a star is less easily torn apart. …Anna Ciurlo (University of California, Los Angeles) and colleagues show in the February 20th Astrophysical Journal that X7 is on its way toward the black hole. It will pass within some 3,200 astronomical units (a.u.; 18 light-days) of Sgr A* in 2036. Already, the cloud is stretching out: it’s now nine times as long as it is wide. …The fact that X7 won’t survive its upcoming pass puts a limit on its age. Its orbit is only 170 years long, so the cloud can’t be more than that many years old. Ciurlo’s team therefore suggests that the gas was ejected recently when a pair of stars collided….

2023-01-14. 850-year-old Supernova Left “Zombie Star” Behind. [] By Govert Schilling, Sky & Telescope. Excerpt: A supernova explosion that skywatchers in the Far East observed almost 850 years ago has produced the most unusual remnant astronomers have ever found. …a paper has been submitted to Astrophysical Journal Letters (preprint available here). In other work presented at the AAS meeting and submitted to Monthly Notices of the Royal Astronomical Society (preprint here), his coauthor Bradley Schaefer (Louisiana State University) argues that the supernova resulted when two white dwarf stars collided, leaving an extremely energetic “zombie” star behind. …the measured expansion velocity of the nebula — some 1,100 kilometers per second — puts its age at 850 years old. …astronomers are now confident about its relation with SN1181, a zero-magnitude supernova that appeared in northern Cassiopeia on August 6th of 1181 AD. Chinese and Japanese observers recorded this “guest star” slowly fading over a period of six months….

2022-06-10. Astronomers may have detected a ‘dark’ free-floating black hole. [] By Robert Sanders, UC Berkeley News. Excerpt: If, as astronomers believe, the death of large stars leave behind black holes, there should be hundreds of millions of them scattered throughout the Milky Way galaxy. The problem is, isolated black holes are invisible. Now, a team led by University of California, Berkeley, astronomers has for the first time discovered what may be a free-floating black hole by observing the brightening of a more distant star as its light was distorted by the object’s strong gravitational field — so-called gravitational microlensing. The team, led by graduate student Casey Lam and Jessica Lu, a UC Berkeley associate professor of astronomy, estimates that the mass of the invisible compact object is between 1.6 and 4.4 times that of the sun. Because astronomers think that the leftover remnant of a dead star must be heavier than 2.2 solar masses in order to collapse to a black hole, the UC Berkeley researchers caution that the object could be a neutron star instead of a black hole. Neutron stars are also dense, highly compact objects, but their gravity is balanced by internal neutron pressure, which prevents further collapse to a black hole. …“This is the first free-floating black hole or neutron star discovered with gravitational microlensing,” Lu said. …The analysis by Lam, Lu and their international team has been accepted for publication in The Astrophysical Journal Letters. …Notably, a competing team from the Space Telescope Science Institute (STScI) in Baltimore analyzed the same microlensing event and claims that the mass of the compact object is closer to 7.1 solar masses and indisputably a black hole.… For

2021-07-27. [] – She Changed Astronomy Forever. He Won the Nobel Prize For It. Source: By Ben Proudfoot, The New York Times. Excerpt: [see video] In 1967, [Jocelyn] Burnell made a discovery that altered our perception of the universe. As a Ph.D. student at Cambridge University assisting the astronomer Anthony Hewish, she discovered pulsars — compact, spinning celestial objects that give off beams of radiation, like cosmic lighthouses. 

2020-05-06. Astronomers Discover the Closest Known Black Hole. By Megan Gannon, Smithsonian Magazine. Excerpt: The pair of stars in a system called HR 6819 is so close to us that on a clear night in the Southern Hemisphere, a person might be able to spot them without a telescope. What that stargazer wouldn’t see, though, is the black hole hiding right there in the constellation Telescopium. At just 1,000 light-years away, it is the closest black hole to Earth ever discovered, and it could help scientists find the rest of the Milky Way’s missing black holes. Dietrich Baade, an emeritus astronomer at the European Southern Observatory (ESO) in Germany and co-author of the study in Astronomy & Astrophysics, says the team never set out to find a black hole. They thought the HR 6819 system was a simple binary, made up of two visible stars orbiting each other. But their observations with the MPG/ESO 2.2-meter telescope at ESO’s La Silla Observatory in Chile revealed something stranger: One of the stars orbited an unknown object every 40 days, while the second star revolved around this inner pair. …the unseen object is more than four times the mass of our sun. An object so big yet invisible must be a black hole. …the newfound black hole is not gathering mass from its companion star. Very few examples of this type of “non-interacting” black hole are known in the Milky Way, but this discovery could lead astronomers to reveal a hidden cosmic population. Astronomers have predicted that in our galaxy alone there should be 100 million to 1 billion black holes of stellar mass (meaning black holes that formed when stars collapsed under the influence of their own gravity). But so far they’ve only detected about two dozen of them. “That’s one of the biggest discrepancies in astronomy,” Baade says…. []  See also Astronomers find closest black hole to Earth, hiding in plain sight, By Daniel Clery, Science Magazine []

2019-01-09. Just a Fainting Spell? Or Is Betelgeuse About to Blow? By Dennis Overbye, The New York Times. [] Excerpt: Is Betelgeuse about to blow? Probably not, but astronomers are having fun thinking about it. Over the last three months, the star, which marks the armpit of Orion the hunter, has mysteriously dimmed to less than half its normal brightness, markedly altering one of the great sights of the winter sky. At the beginning of January the star was fainter than ever before observed, according to Edward Guinan of Villanova University, who has been compiling data on Betelgeuse. In its “fainting” spell, Dr. Guinan said, the star has dropped from seventh to twenty-first on the list of brightest stars in the sky. …All this has raised the issue of Betelgeuse’s mortality, and its cosmic endgame. …That will be quite a show. Betelgeuse is only 700 light years from Earth, far enough to not kill us when it goes, but close enough to impress; the supernova would be as bright as a full moon in our sky. …“My money all along has been that Betelgeuse is going through a somewhat extreme, but otherwise normal quasi-periodic change in brightness,” said J. Craig Wheeler, a supernova expert at the University of Texas in Austin…. See also Waiting for Betelgeuse to Explode [

2019-08-19. A Supernova Was Hiding in Antarctica’s Snow. By Katherine Kornei, The New York Times.] Excerpt: Earth is continuously plowing through extraterrestrial dust. Tens of thousands of tons of the stuff, mostly from asteroids and comets, settles all over the planet every year. …Recently, scientists analyzed dust collected from Antarctic snow and found an excess of radioactive iron. After ruling out contamination from nuclear weapons testing and other sources, the team concluded that the iron was produced by supernovas, fleeting explosions of stars more massive than the sun. This discovery suggests that stellar blasts might have rocked Earth and the rest of the solar system in the not-too-distant past. The results were published on Aug. 12 in Physical Review Letters []. Meteorite hunters are drawn to Antarctica because the space rocks, which are dark, stand out against the snow. Dominik Koll, a doctoral candidate in nuclear physics at the Australian National University in Canberra, appreciates Antarctica for other reasons: its remote location and desert climate, which ensure that whatever extraterrestrial dust falls from the sky remains relatively uncontaminated and undiluted. In 2015, a colleague of Mr. Koll’s collected roughly 1,100 pounds of snow near Kohnen Station in Antarctica. …The researchers were looking for a rare, unstable variety of iron containing 26 protons and 34 neutrons. This radioactive isotope, iron-60, is produced by supernovas. …Iron-60 has been found on Earth in oceanic crust that is millions of years old and on the surface of the moon, indications that the isotope circulated through the solar system long ago. But iron-60 from supernovas has never been found in geologically young material; its discovery in relatively fresh snow would suggest that it’s still raining down on Earth…. 

2016-02-11. Gravitational waves, Einstein’s ripples in spacetime, spotted for first time. By Adrian Cho, Science. Excerpt: …two massive black holes—the ultrastrong gravitational fields left behind by gigantic stars that collapsed to infinitesimal points—slowly drew together… spiraled ever closer, until, about 1.3 billion years ago, they whirled about each other at half the speed of light and finally merged. The collision sent a shudder through the universe: ripples in the fabric of space and time called gravitational waves. Five months ago, they washed past Earth. And, for the first time, physicists detected the waves, fulfilling a 4-decade quest and opening new eyes on the heavens. The discovery marks a triumph for the 1000 physicists with the Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of gigantic instruments in Hanford, Washington, and Livingston, Louisiana. …Albert Einstein predicted the existence of gravitational waves 100 years ago, but directly detecting them required mind-boggling technological prowess …[sensing] a wave that stretched space by one part in 1021, making the entire Earth expand and contract by 1/100,000 of a nanometer, about the width of an atomic nucleus….. — see also New York Times video and article, MIT News story, and Remembering Joseph Weber, the controversial pioneer of gravitational waves. Watch a recorded seminar given by physicist Daniel Holz to a group at Lawrence Berkeley National Laboratory.

2015-06-17. Traces of Earliest Stars That Enriched Cosmos Are Spied. By Dennis Overbye, New York Times. Excerpt: Astronomers said Wednesday that they had discovered a lost generation of monster stars that ushered light into the universe after the Big Bang and jump-started the creation of the elements needed for planets and life before disappearing forever. …in the aftermath of the Big Bang only hydrogen, helium and small traces of lithium were available to make the first stars. Such stars could have been hundreds or thousands of times as massive as the sun, according to calculations, burning brightly and dying quickly, only 200 million years after the universe began. Their explosions would have spewed into space the elements that started the chain of thermonuclear reactions by which subsequent generations of stars have gradually enriched the cosmos with elements like oxygen, carbon and iron. …in a paper to be published in The Astrophysical Journal, an international crew of astronomers led by David Sobral of the University of Lisbon, in Portugal, and the Leiden Observatory, in the Netherlands, said they had spotted the signature of these first-generation stars in a recently discovered galaxy that existed when the universe was only about 800 million years old. …The galaxy, known as CR7, is three times as luminous as any previously found from that time, the authors said. Within it is a bright blue cloud that seems to contain only hydrogen and helium….

2015-03-05. Astronomers Watch a Supernova and See Reruns. By Dennis Overbye, The New York Times. Excerpt: …astronomers using the Hubble Space Telescope say they have been watching the same star blow itself to smithereens in a supernova explosion over and over again, thanks to a trick of Einsteinian optics. The star exploded more than nine billion years ago on the other side of the universe, too far for even the Hubble to see without special help from the cosmos. …light rays from the star have been bent and magnified by the gravity of an intervening cluster of galaxies so that multiple images of it appear. Four of them are arranged in a tight formation known as an Einstein Cross surrounding one of the galaxies in the cluster.  …This is the first time astronomers have been able to see the same explosion over and over again, and its unique properties may help them better understand not only the nature of these spectacular phenomena but also cosmological mysteries like dark matter and how fast the universe is expanding…. “I was sort of astounded,” said Patrick Kelly of the University of California, Berkeley, who discovered the supernova images in data recorded by the space telescope in November …lead author of a report describing the supernova published on Thursday in the journal Science. …Robert Kirshner, a supernova expert at the Harvard-Smithsonian Center for Astrophysics who was not involved in the work, said: “We’ve seen gravitational lenses before, and we’ve seen supernovae before. We’ve even seen lensed supernovae before. But this multiple image is what we have all been hoping to see.”….

2012 Jan 11. Hubble Solves Mystery on Source of Supernova in Nearby Galaxy. News Release Number: STScI-2012-06, Hubblesite.  Summary: Using NASA’s Hubble Space Telescope, astronomers have solved a longstanding mystery on the type of star, or so-called progenitor, that caused a supernova in a nearby galaxy. The finding yields new observational data for pinpointing one of several scenarios that could trigger such outbursts. Based on previous observations from ground-based telescopes, astronomers knew that a kind of supernova called a Type Ia created a remnant named SNR 0509-67.5, which lies 170,000 light-years away in the Large Magellanic Cloud galaxy. The type of system that leads to this kind of supernova explosion has long been a high importance problem with various proposed solutions but no decisive answer. All these solutions involve a white dwarf star that somehow increases in mass to the highest limit. Astronomers failed to find any companion star near the center of the remnant, and this rules out all but one solution, so the only remaining possibility is that this one Type Ia supernova came from a pair of white dwarfs in close orbit. 

2011 Oct 24. NASA Telescopes Help Solve Ancient Supernova Mystery. JPL News.  Excerpt:A mystery that began nearly 2,000 years ago, when Chinese astronomers witnessed what would turn out to be an exploding star in the sky, has been solved. New infrared observations from NASA’s Spitzer Space Telescope and Wide-field Infrared Survey Explorer, or WISE, reveal how the first supernova ever recorded occurred and how its shattered remains ultimately spread out to great distances. The findings show that the stellar explosion took place in a hollowed-out cavity, allowing material expelled by the star to travel much faster and farther than it would have otherwise. “This supernova remnant got really big, really fast,” said Brian J. Williams, an astronomer at North Carolina State University in Raleigh. Williams is lead author of a new study detailing the findings online in the Astrophysical Journal. “It’s two to three times bigger than we would expect for a supernova that was witnessed exploding nearly 2,000 years ago. Now, we’ve been able to finally pinpoint the cause.” …The observations also show … that a white dwarf can create a cavity around it before blowing up in a Type Ia event. A cavity would explain why the remains of RCW 86 are so big. When the explosion occurred, the ejected material would have traveled unimpeded by gas and dust and spread out quickly. Spitzer and WISE allowed the team to measure the temperature of the dust making up the RCW 86 remnant at about minus 325 degrees Fahrenheit, or minus 200 degrees Celsius. They then calculated how much gas must be present within the remnant to heat the dust to those temperatures. The results point to a low-density environment for much of the life of the remnant, essentially a cavity….

2010 May. Hypervelocity Stars -Observations-  Lecture by Dr. Warren Brown, Harvard Smithsonian Center for Astrophysics

2010 Feb 22. From the Clash of White Dwarfs, the Birth of a Supernova. By Dennis Overbye, NY Times. Excerpt: …For the last 20 years, astronomers seeking to measure the cosmos have used a special type of exploding star, known as Type 1a supernovas, as distance markers. They are thought to result when stars known as white dwarfs grow beyond a certain weight limit, setting off a thermonuclear cataclysm that is not only bright enough to be seen across the universe but is also remarkably uniform from one supernova to the next. Using them, two teams of astronomers a little more than a decade ago reached the startling and now widely held conclusion that some “dark energy” was speeding up the expansion of the universe.
But astronomers, to their embarrassment, have not been able to agree on how the white dwarf gains its fatal weight and explodes, whether by slowly grabbing material from a neighboring star or by crashing into another white dwarf.
In a telephone news conference on Wednesday and a paper published Thursday in the journal Nature, Marat Gilfanov and his colleague, Akos Bogdan, both of the Max Planck Institute for Astrophysics in Garching, Germany, said that for at least one class of galaxies in the universe, the roundish conglomerations of older, redder stars known as ellipticals, these supernovas are mostly produced by collisions.
“We have revealed the source of the most important explosions in cosmology,” Dr. Gilfanov said, adding that until now “we didn’t know exactly what they were.”…

2009 Nov 6. Supernova fits into a new class. By David Perlman, Chronicle Science Editor.  Excerpt: (11-05) 19:12 PST SAN FRANCISCO — A bizarre exploding star that left its embers glowing invisibly in the distant sky …. The record examined by Dovi Poznanski, a UC Berkeley researcher, revealed that the short-lived but violent cosmic explosion in a far-off galaxy 135 million light-years away could be an entirely new class of supernovae…. This unique supernova, dubbed SN2002bj, was the first one found that was apparently caused when helium gas flowed from one tiny but immensely massive white dwarf star to another dwarf star orbiting close by. The result was a true thermonuclear explosion that died away in days rather than months, the Berkeley astronomers said, and its formation differed sharply from standard supernova models.
…Poznanski calculated that at the explosion’s most powerful moment, it must have flared 10 billion times brighter than our sun, although nowhere near as bright as normal supernovae that can blaze 10 times more powerfully than that. …The story of SN2002bj’s detection actually started with a competition involving two amateur astronomers: Tim Puckett of Atlanta, who operates his own automated high-tech observatory in the little Georgia town of Ellijay (population 1,119), and Jack Newton, who has a high-tech robot telescope in Portal, Ariz. (population 80). They lead an amateur World Supernova Search Team, whose 28 members – from Canada to South Africa – use their high-powered telescopes to scan the skies every clear night. The team has discovered no fewer than 206 supernovae in the past 15 years.
Puckett and Newton discovered SN2002bj at the same time the night it flared, and immediately reported it to the International Astronomical Union’s Central Bureau for Astronomical Telegrams at the Harvard Smithsonian Astrophysical Observatory in Cambridge, Mass., on April 18, 2002.
Alex Filippenko, a senior UC astronomer whose team also hunts for supernovae with a robot telescope system at Lick Observatory atop Mount Hamilton, also reported detecting the stellar explosion on the same night – but just a little later. “It really was a dead heat,” Filippenko said of the discovery. But he conceded that Puckett and Newton beat him technically” by three and a half hours because Puckett’s observatory is located where the time is three hours ahead and where the sun sets much earlier….

2008 November/December. Blown apart. BY KEAY DAVIDSON.  Excerpt: …Saul Perlmutter … “Our brains are…so good at seeing patterns that we sometimes see patterns that aren’t there.”
Perlmutter and his colleagues have spent two decades looking for patterns in the night sky-specifically, patterns in the spatial distribution of distant, dying stars that suddenly brighten, and then fade. They hope to resolve an ancient puzzle: How will the universe end? Eleven years ago, in the autumn of 1997, they uncovered a big piece of the puzzle. But their discovery was so unexpected that they worried the patterns were illusory. They checked and rechecked their data, searching for some subtle error that might have misled them. A mistake would make them look like fools. But if they waited too long to report their results, rival teams might beat them to announcing the discovery and perhaps to winning a Nobel Prize.
Their shocking discovery was “dark energy,” a mysterious repulsive force that apparently makes the universe expand faster and faster over time. Dark energy now threatens to undermine fundamental beliefs about physics, cosmology, perhaps even the nature of scientific discovery….
…when Perlmutter arrived at Berkeley as a graduate student in physics in the early 1980s, he hoped to do research “that would address a deep philosophical question.” His doctoral adviser was physicist Richard A. Muller, who was planning to use robotic telescopes to look for supernovae and a hypothetical star called Nemesis, which Muller suspected triggered mass extinctions on Earth by steering comets toward the inner solar system every 26 million years. Perlmutter joined that project, where physicist Carl Pennypacker was developing a robotic telescopic search at Berkeley’s Leuschner Observatory in Lafayette. Over the next few years, their hard-working robot observer detected 20 “nearby” supernovae. Although the mystery star was never found, the supernova investigations opened the long, winding road to a historic discovery….

2008 December 4. Study Illuminates Star Explosion From 16th Century. The New York Times.  Excerpt: NEW YORK (AP) — More than 400 years after Danish astronomer Tycho Brahe challenged established wisdom about the heavens by analyzing a strange new light in the sky, scientists say they’ve finally nailed down just what he saw.
It’s no big surprise. Scientists have known the light came from a supernova, a huge star explosion. But what kind of supernova?
A new study confirms that, as expected, it was the common kind that involves the thermonuclear explosion of a white dwarf star with a nearby companion.
…The story of what’s commonly called Tycho’s supernova began on Nov. 11, 1572, when Brahe was astonished to see what he thought was a brilliant new star in the constellation Cassiopeia. The light eventually became as bright as Venus and could be seen for two weeks in broad daylight. After 16 months, it disappeared.
Working before telescopes were invented, Brahe documented with precision that unlike the moon and the planets, the light’s position didn’t move in relation to the stars. That meant it lay far beyond the moon. That was a shock to the contemporary view that the distant heavens were perfect and unchanging.
…The direct light from the supernova swept past Earth long ago. But some of it struck dust clouds in deep space, causing them to brighten. That ”light echo” was still observable, and the new study was based on analyzing the wavelengths of light from that….

2008 May 21. X-RAY OUTBURST LEADS TO ALL-OUT STUDY OF SUPERNOVA. by Robert Sanders.  NASA’s Swift satellite caught the rare birth of a supernova earlier this year, allowing astronomers to rapidly deploy ground-based telescopes to follow its evolution and learn about normal stellar explosions. UC Berkeley astronomers have analyzed the data to conclude that the original star was more than 30 times the mass of the sun, but only slightly larger, when its core ran out of fuel and imploded, blowing the star to smithereens.

2008 May 14. DISCOVERY OF MOST RECENT SUPERNOVA IN OUR GALAXY. NASA RELEASE: 08-126. Excerpt: WASHINGTON  — The most recent supernova in our galaxy has been discovered by tracking the rapid expansion of its remains. This result, using NASA’s Chandra X-ray Observatory and the National Radio Astronomy Observatory’s Very Large Array, will help improve our understanding of how often supernovae explode in the Milky Way galaxy.

2006 July 21. Hypervelocity stars. New Scientist magazine podcast leads with an interview Dr. Warren Brown discussing hypervelocity star discoveries. Companion article: “Black Holes Don’t Eat Everything” — cover-story of the July 22, 2006 issue of New Scientist magazine.

2006 Jan 27. Podcast interview on Hypervelocity Stars. Fraser Cain, of the space-news site Universe Today interviews Dr. Warren Brown regarding the early hypervelocity star discoveries.