Another Night, Another Supernova

Supernova 2020jfo in M61 is not the only supernova occurring at the moment. Actually there are over sixty supernova in progress at the moment that we know of. The modern transient search programs locate them by the dozens, and while the average large galaxy might have one supernova a century, there are an enormous number of galaxies we can observe while monitoring for those great explosions.

Currently the brightest supernova is 2020hvf at magnitude 12.4 hosted by galaxy NGC3643 in Leo. Unlike the pretty face-on spiral of M61, this small 14th magnitude galaxy is completely outshone by the supernova. Looking at the image one is struck by the realization that for a week or two that one star is outshining the combined light of the hundreds of billions of other stars that make up an entire galaxy.

NGC3643 with supernova SN2020hvf on the evening of Mar 15, 2020
NGC3643 with supernova SN2020hvf on the evening of Mar 15, 2020

M61 with a Supernova

M61 has been particularly bountiful when it comes to exploding stars. This should not be a huge surprise as M61 is also experiencing rapid star formation. With a lot of new stars around some of the largest stars will die early and die big.

Early this month the Zwicky Transient Facility noted a new supernova in M61, now cataloged as SN2020jfo. This explosion is now visible at 14.7 magnitude and can be seen by modest amateur telescope of at least 8-10 inches aperture.

Eight supernovae have now been observed in M61: SN 2020jfo, SN 2014dt, SN 2008in, SN 2006ov, SN 1999gn, SN 1964F, SN 1961I, and SN 1926A, an unusual number for any galaxy. In contrast our Milky Way galaxy last experienced a supernova in 1604.

Between shooting other targets I stopped by M61 last night to take a few exposures of the galaxy and see this supernova for myself.

NGC4303 - M61 with supernova SN2020jfo on the evening of Mar 14, 2020
NGC4303 – M61 with supernova SN2020jfo on the evening of Mar 14, 2020

Astronomers Discover A Star That Would Not Die

W. M. Keck Observatory press release

An international team of astronomers led by Las Cumbres Observatory (LCO) has made a bizarre discovery; a star that refuses to stop shining.

Supernovae, the explosions of stars, have been observed in the thousands and in all cases they marked the death of a star.

Artists impression of a supernova. Credit NASA/ESA/G. Bacon (STSCI)
But in a study published today in the journal Nature, the team discovered a remarkable exception; a star that exploded multiple times over a period of more than fifty years. Their observations, which include data from W. M. Keck Observatory on Maunakea, Hawaii, are challenging existing theories on these cosmic catastrophes.

“The spectra we obtained at Keck Observatory showed that this supernova looked like nothing we had ever seen before. This, after discovering nearly 5,000 supernovae in the last two decades,” said Peter Nugent, Senior Scientist and Division Deputy for Science Engagement in the Computational Research Division at Lawrence Berkeley National Laboratory who co-authored the study. “While the spectra bear a resemblance to normal hydrogen-rich core-collapse supernova explosions, they grew brighter and dimmer at least five times more slowly, stretching an event which normally lasts 100 days to over two years.”

Researchers used the Low Resolution Imaging Spectrometer (LRIS) on the Keck I telescope to obtain spectrum of the star’s host galaxy, and the Deep Imaging and Multi-Object Spectrograph (DEIMOS) on Keck II to obtain high-resolution spectra of the unusual star itself.

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Supernova Split into Four Images by Cosmic Lens

W. M. Keck Observatory press release

Astronomers have for the first time spotted four images of a distant exploding star, arranged in a cross-shape pattern by a powerful gravitational lens. In addition to being a unique sighting, the discovery will provide insight into the distribution of dark matter. The findings will appear March 6 in a special issue of the journal Science, celebrating the centenary of Albert Einstein’s Theory of General Relativity.

This image shows the light of a supernova split into four images by a foreground elliptical galaxy embedded in a giant cluster of galaxies. The four images were spotted on Nov. 11, 2014. Credit: NASA/ESA
Two teams spent a week analyzing the object’s light, confirming it was the signature of a supernova, then turned to the W. M. Keck Observatory on Mauna Kea, in Hawaii, to gather critical measurements including determining the distance to the supernova’s host galaxy 9.3 billion light-years from Earth.

To explain the unique, four-up projection, the scientists determined a galaxy cluster and one of its massive elliptical members are gravitationally bending and magnifying the light from the supernova behind it, through an effect called gravitational lensing. First predicted by Albert Einstein, this effect is similar to a glass lens bending light to magnify and distort the image of an object behind it. The multiple images, arranged around the massive elliptical galaxy, form an Einstein Cross, a name originally given to a multiple-lensed quasar that appear as a cross.

Although astronomers have discovered dozens of multiply imaged galaxies and quasars, they have never seen a stellar explosion resolved into several images. “It really threw me for a loop when I spotted the four images surrounding the galaxy – it was a complete surprise,” said Patrick Kelly of the University of California, Berkeley, lead author of the paper and a member of the Grism Lens Amplified Survey from Space (GLASS) collaboration. The GLASS group is working with the FrontierSN team to analyze the supernova.

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Supernova Ejects Galaxy’s Fastest Star

W. M. Keck Observatory press release

Scientists using the W. M. Keck Observatory and Pan-STARRS1 telescopes on Hawaii have discovered a star that breaks the galactic speed record, traveling with a velocity of about 1,200 kilometers per second or 2.7 million miles per hour. This velocity is so high, the star will escape the gravity of our galaxy. In contrast to the other known unbound stars, the team showed that this compact star was ejected from an extremely tight binary by a thermonuclear supernova explosion. These results will be published in the March 6 issue of Science.

US 708 Supernova Ejected Star
An artist impression of the mass-transfer phase followed by a double-detonation supernova that leads to the ejection of US 708. Credit: ESA/Hubble, NASA, S. Geier
Stars like the Sun are bound to our Galaxy and orbit its center with moderate velocities. Only a few so-called hypervelocity stars are known to travel with velocities so high that they are unbound, meaning they will not orbit the galaxy, but instead will escape its gravity to wander intergalactic space.

A close encounter with the supermassive black hole at the centre of the Milky Way is typically presumed the most plausible mechanism for kicking these stars out of the galaxy.

A team of astronomers led by Stephan Geier (European Southern Observatory, Garching) observed the known high-velocity star know as US 708 with the Echellette Spectrograph and Imager instrument on the 10-meter, Keck II telescope to measure its distance and velocity along our line of sight. By carefully combining position measurements from digital archives with newer positions measured from images taken during the course of the Pan-STARRS1 survey, they were able to derive the tangential component of the star’s velocity (across our line of sight).

Putting the measurements together, the team determined the star is moving at about 1,200 kilometers per second – much higher than the velocities of previously known stars in the Milky Way galaxy. More importantly, the trajectory of US 708 means the supermassive black hole at the galactic center could not be the source of US 708’s extreme velocity.

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Aussie Scientist Finds Rare Supernova at Keck Observatory

W. M. Keck Observatory press release by Dr. Duncan Forbes…

It was a dark and stormy night in the city of Angels. Well, actually it wasn’t. But more on that later…

It was a clear night on the summit of Mauna Kea at Keck Observatory on the 20th March. My colleagues and I were using the Echellette Spectrograph and Imager (ESI) instrument, which looks at faint objects in the visible wavelengths, to study star clusters and small galaxies.

Can you spot the supernova? Supernova SN2014ai on March 20th, 2014
I was actually in our special ‘remote ops’ room at Swinburne University, with my postdoc, Joachim Janz. This is a room decked out with a computer, a backup computer, a video-link to Keck Observatory and a dedicated Internet connection. As we are 21 hours ahead of Hawaii, it was a Friday afternoon when we started observing that Thursday night. My colleagues Sam Penny and Mark Norris were in the Keck control room, and Aaron Romanowsky was in his remote ops room at UC Santa Cruz.

Shortly into our night’s observing, we noticed a bright source in the guide camera image that wasn’t on our finding chart of that region. Still we managed to find our target and took a spectrum of it. But we decided to go back and see if that `new’ bright source was still there. Sure enough it was and it hadn’t moved. It was probably a supernova (or an asteroid coming straight at us!), so I decided to get a 5min spectrum with ESI. And indeed we had found a supernova—a type Ia to be exact. Type Ia supernovae are fairly rare in the nearby Universe and represent the explosion of at least one white dwarf star in a binary system. It is this same type of supernova that led to the discovery of Dark Energy in the Universe using the Keck Observatory, and three Nobel prizes.

Our supernova is located in the outskirts of a galaxy some 100 million light years from us—so it exploded 100 million years ago but the light only reached us that night.

I later found out that an automated telescope on the Palomar Mountain overlooking Los Angeles detected the supernova shortly before us. They also managed to get a spectrum but that was taken after our Keck II/ESI spectrum. The exciting thing is that both the Palomar Observatory and ourselves managed to observe the supernova in the 1-2 weeks before it reaches its maximum brightness (and then fades steadily after that).

The supernova has been given the designation SN2014ai.

All in all, not bad for a late night at the office…

Duncan Forbes is a professor of astronomy at Swinburne University in Melbourne, Australia, and a 2014 Evenings with Astronomers presenter at the signature Friends of Keck lecture series. Swinburne astronomers are awarded time for their research on Keck Observatory through an agreement with the California Institute of Technology.

Postcard from the Universe – M82 with SN2014J

The brightest nearby supernova in may years is currently visible in the bright galaxy M82. I did want to photograph the supernova before it fades much more. It apparently reached a maximum brightness of magnitude 10.5 a few days ago and is starting to dim. But has so far only slid a few tenths of a magnitude.

So I tried to photograph a supernova, and Murphy came to visit.

The last week has seen me dealing with a sinus infection, which combined with terrible weather has kept me from setting up in the driveway for photography. Taking advantage of a few clear hours last night I did make an attempt. Things continued to go wrong.

A high thin haze would not go away, lit up by the light of a bright quarter moon it created high background and gradients in the imagery that would not calibrate out. I forgot to install the LPS filter, meaning that the low pressure sodium lighting of the village compounded the moonlight in creating a poor signal to noise and bad gradients. The autoguider would not behave. This was eventually solved by adjusting the tuning parameters in PHD guide. Not before ruining most of my exposures, I ended up throwing out 24 of 32 exposures. When I did get everything figured out and corrected, and the Moon had fianlly set, the clouds rolled back in.

The final eight usable exposures did result in a somewhat acceptable final product. It could have been so much better…

M81 & M82 with SN2014J
The galaxies M81 & M82 with SN2014J seen in the disk M82 at top

Caltech Scientists Detects First Progenitor of Type 1b Supernova

W. M. Keck Observatory press release

Powerful new survey telescopes led by the California Institute of Technology (Caltech) are being combined with the W. M. Keck Observatory to provide insight into rare, exotic cosmic explosions. Caltech’s intermediate Palomar Transient Factory (iPTF) recently described the first direct detection of the progenitor of a rare type of supernova in a nearby galaxy. The findings were published n the September 20 issue of Astrophysical Journal Letters [].

The paper describes the detection of a Type Ib supernova, a rare explosion in which the progenitor star lacks an outer layer of hydrogen, the most abundant element in the universe. It has proven difficult to pin down which kinds of stars give rise to Type Ib supernovae. One of the most promising ideas, according to graduate student and lead author Yi Cao, is they originate from Wolf-Rayet stars. These objects are 10 times more massive and thousands of times brighter than the Sun and have lost their hydrogen envelope by means of very strong stellar winds. Until recently, no solid evidence existed to support this theory. Cao and colleagues believe that the young supernova they discovered, iPTF13bvn, occurred at a location formerly occupied by a likely Wolf-Rayet star.

Supernova iPTF13bvn was spotted on June 16, less than a day after the onset of its explosion. With the aid of the world-leading adaptive optics system installed on the Keck II telescope, one of Keck Observatory’s two 10-meter telescopes in Hawaii, the team obtained a high-resolution image of this supernova to determine its precise position. Then they compared the Keck Observatory image to a series of pictures of the same galaxy (NGC 5806) taken by the Hubble Space Telescope in 2005, and found one starlike source spatially coincident to the supernova. Its intrinsic brightness, color, and size — as well as its mass-loss history, inferred from supernova radio emissions — were characteristic of a Wolf-Rayet star.

“All evidence is consistent with the theoretical expectation that the progenitor of this Type Ib supernova is a Wolf-Rayet star,” said Cao. “Our next step is to check for the disappearance of this progenitor star after the supernova fades away. We expect that it will have been destroyed in the supernova explosion.”

Though Wolf-Rayet progenitors have long been predicted for Type Ib supernova, the new work represents the first time researchers have been able to fill the gap between theory and observation, according to study coauthor and Mansi Kasliwal from the Carnegie Institution for Science. “This is a big step in our understanding of the evolution of massive stars and their relation to supernovae,” she said.

The iPTF builds on the legacy of the Caltech-led Palomar Transient Factory (PTF), designed in 2008 to systematically chart the transient sky by using a robotic observing system mounted on the 48-inch Samuel Oschin Telescope on Palomar Mountain near San Diego, California. This state-of-the-art, robotic telescope scans the sky rapidly over a thousand square degrees each night to search for transients.

Postcard from the Universe – NGC1365 and Supernova 2012fr

A photo taken from my driveway of NGC1365 and supernova 2012fr. It is a bright supernova in a classic barred spiral galaxy. I had observed NGC1365 in mid-October with the 18″, noting the beautiful spiral structure. The supernova appeared about two weeks later. I have since observed it in a couple telescopes, including Cliff’s 24″.

The nova seems to be fading now, it peaked around 12th magnitude in November. Currently about 14.5 magnitude, but still easy with the AT6RC and Canon 20Da camera.

NGC1365 and SN2012fr
The barred spiral galaxy NGC1365 and SN2012fr

Swinburne Team on Keck Discovers Farthest Supernova Ever

W. M Keck Observatory press release

Two ‘super-luminous’ supernovae — stellar explosions 10–100 times brighter than other supernova types — have been detected in the distant Universe, using the W.M. Keck Observatory on the top of Mauna Kea in Hawaii. The discovery, reported online in Nature this week, sets a record for the most distant supernova yet detected, and offers the rare possibility of observing the explosions of the first stars to form after the Big Bang.

Early Supernova
Simulation of a galaxy hosting a super-luminous supernova and its chaotic environment in the early Universe. Credit: Adrian Malec and Marie Martig (Swinburne University)
“The type of supernovae we’ve found are extremely rare,” said Jeff Cooke, astrophysicist at Swinburne University of Technology, whose team made the discovery. “In fact, only one has been discovered prior to our work. This particular type of supernova results from the death of a very massive star (about 100 – 250 times the mass of our Sun) and explodes in a completely different way compared to other supernovae. Discovering and studying these events provides us with observational examples to better understand them and the chemicals they eject into the Universe when they die.”

Super-luminous supernovae were discovered only a few years ago, and are rare in the nearby Universe. Their origins are not well understood, but a small subset of them is thought to occur when extremely massive stars undergo a nuclear explosion triggered by the conversion of photons into electron–positron pairs. Such events are expected to have occurred more frequently in the early Universe (at high redshift), when massive stars were more common. This, and the extreme brightness of these events, encouraged Cooke and colleagues to search for super-luminous supernovae at redshifts, z, greater than 2, when the Universe was less than one-quarter of its present age.

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