Supernova discovered in Cartwheel galaxy

Cartwheel Galaxy, before and after supernova
Click for full image.

Cool image time! In reviewing a December 2021 image of the Cartwheel Galaxy taken by the New Technology Telescope in Chile, astronomers noticed something that was not there in earlier images, a new supernovae.

The photo above, reduced to post here, compares a 2014 image, taken by the Very Large Telescope, with the 2021 photo. In the lower left of the new image is a bright object not in the previous photo.

This event, called SN2021afdx, is a type II supernova, which occurs when a massive star reaches the end of its evolution. Supernovae can cause a star to shine brighter than its entire host galaxy and can be visible to observers for months, or even years — a blink of an eye on astronomical timescales. Supernovae are one of the reasons astronomers say we are all made of stardust: they sprinkle the surrounding space with heavy elements forged by the progenitor star, which may end up being part of later generations of stars, the planets around them and life that may exist in those planets.

Cartwheel is about 500 million light years away, and because of its bright outer ring is one one of the more unusual nearby galaxies.

New data makes past nova too bright, but not bright enough to be supernova

The uncertainty of science: Astronomers, using new data from the Gemini North ground-based telescope, have found that a star that brightened in 1670 and was labeled a nova is much farther away than previously thought, which means that 1670 eruption was far too powerful for a nova, but not powerful enough to make it a supernova.

By measuring both the speed of the nebula’s expansion and how much the outermost wisps had moved during the last ten years, and accounting for the tilt of the nebula on the night sky, which had been estimated earlier by others, the team determined that CK Vulpeculae lies approximately 10,000 light-years distant from the Sun — about five times as far away as previously thought. That implies that the 1670 explosion was far brighter, releasing roughly 25 times more energy than previously estimated [4]. This much larger estimate of the amount of energy released means that whatever event caused the sudden appearance of CK Vulpeculae in 1670 was far more violent than a simple nova.

“In terms of energy released, our finding places CK Vulpeculae roughly midway between a nova and a supernova,” commented Evans. “[T]he cause — or causes — of the outbursts of this intermediate class of objects remain unknown. I think we all know what CK Vulpeculae isn’t, but no one knows what it is.”

Recent research has also suggested that the cause of the eruption was not from the interaction of a binary system with one normal star and a white dwarf, as believed for decades, but possibly a binary system with a brown dwarf, or a red giant star, or two normal stars. All are remain possible, none however have been confirmed.

Astronomers claim to have discovered most powerful supernova ever

The uncertainty of science: Astronomers have now calculated that a supernova that was spotted in 2016 was possibly the brightest ever detected, and might have been caused by the merger of two massive stars, each about sixty times as massive as the Sun.

SN 2016aps was discovered by the Panoramic Survey Telescope and Rapid Response System (Pan- STARRS) Survey for Transients on February 22, 2016 with an apparent magnitude of 18. Also known as PS16aqy, the explosion occurred in a low-mass galaxy some 3.1 billion light-years from Earth.

University of Birmingham’s Dr. Matt Nicholl and colleagues believe SN 2016aps could be an example of an extremely rare ‘pulsational pair-instability’ supernova, possibly formed from two massive stars that merged before the explosion. Such an event so far only exists in theory and has never been confirmed through astronomical observations.

…The researchers observed SN 2016aps for two years, until it faded to 1% of its peak brightness. Using these measurements, they calculated the mass of the supernova was between 50 to 100 solar masses. Typically supernovae have masses of between 8 and 15 solar masses.

They theorize that the supernova became especially bright when the explosion collided with a gas shell that already surrounded both stars.

Lots of assumptions and guesswork here, based on a tiny amount of data. The biggest lack is that they don’t have any observations of the star (or stars) prior to the supernova, so any theory about what those stars were like is exactly that, a theory.

Images reveal changes in Betelgeuse’s shape as it has been dimming

Betelgeuse dimmed
Click for full image.

Using the Very Large Telescope in Chile astronomers have produced before and after images of the red giant Betelgeuse, showing the changes to the star in the past year as it has dimmed by about 36%.

The image to the right, cropped and reduced to post here, was taken in December and shows the star in its dimmed state. Below the fold is a short video that compares this image with a photograph taken in January 2019. The star was then more spherical and evenly bright.

Betelgeuse’s misshaped profile and uneven brightness is not actually a new thing. See for example this 2017 image, where I noted that the bulge on the star’s side suggested “that continuous observations would reveal the outer atmosphere waxing and waning almost like the stuff inside a lava lamp.” The star is a giant gasbag that in the past has frequently been observed with dark patches on its surface and a sense that it is not always spherical. Those changes however have not occurred with such a significant dimming, a full magnitude

In late December I had posted a story noting that the dimming appeared to be expected, caused by the alignment of two different regular fluctuations of brightness, one 5.9 years long and the other 0.5 year long. It was expected that the star would begin brightening again.

Right now astronomers estimate that the low point in these cycles will occur on approximately February 21st. If the star begins to brighten following that date it would confirm that this dimming is just part of its cycles. If not, then it could be that we are in the preliminaries to a supernova event that would probably make Betelgeuse bright enough to be seen during the day.
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The 1572 Tycho supernova, as seen by Chandra

Remnant of Tycho's supernova

Cool image time! The Chandra science team has released a beautiful X-ray image of the remnant from the 1572 supernova first discovered by astronomer Tycho Brahe.

As with many supernova remnants, the Tycho supernova remnant, as it’s known today (or “Tycho,” for short), glows brightly in X-ray light because shock waves — similar to sonic booms from supersonic aircraft — generated by the stellar explosion heat the stellar debris up to millions of degrees. In its two decades of operation, NASA’s Chandra X-ray Observatory has captured unparalleled X-ray images of many supernova remnants.

Chandra reveals an intriguing pattern of bright clumps and fainter areas in Tycho. What caused this thicket of knots in the aftermath of this explosion? Did the explosion itself cause this clumpiness?

The image to the right, reduced to post here, is a composite of both X-ray (the remnant) and optical light (the background stars).

Star becomes black hole without supernova explosion

The uncertainty of science: Astronomers think they have identified a star that, rather than die and become a black hole in a supernova explosion, merely fizzled into a black hole.

Starting in 2009, one particular star in the Fireworks Galaxy, named N6946-BH1, began to brighten weakly. By 2015, it appeared to have winked out of existence. The astronomers aimed the Hubble Space Telescope at the star’s location to see if it was still there but merely dimmed. They also used the Spitzer Space Telescope to search for any infrared radiation emanating from the spot. That would have been a sign that the star was still present, but perhaps just hidden behind a dust cloud.

All the tests came up negative. The star was no longer there. By a careful process of elimination, the researchers eventually concluded that the star must have become a black hole.

There are a lot of uncertainties here. Nonetheless, astronomers have theorized that some stars could collapse into black holes with any explosions, and it appears they might have found their first example of that.

Astronomers successfully predict appearance of supernova

For the first time ever astronomers have been able to predict and photograph the appearance of a supernova, its light focused by the gravitational lensing caused by a galaxy and the dark matter that surrounds it.

The NASA/ESA Hubble Space Telescope has captured the image of the first-ever predicted supernova explosion. The reappearance of the Refsdal supernova was calculated from different models of the galaxy cluster whose immense gravity is warping the supernova’s light.

What makes this significant is that the prediction models were based on the theory of gravitational lensing and required the presence of dark matter to work. That they worked and were successful in predicting the appearance of this gravitationally bent light (bent by the dark matter it passed through) is a very strong confirmation of both concepts. Up until now I have been somewhat skeptical of gravitational lensing. This confirmation removes some of that skepticism.

The supernova of 1987 finally begins to fade

Almost thirty years after Supernova 1987a became the first naked eye supernova since the invention of the telescope, the necklace ring of spots that the explosion’s shockwave ignited in the late 1990s are finally beginning to fade.

But now the hotspots have slowly begun to fade, Claes Fransson (Stockholm University, Sweden) and colleagues report in the June 10th Astrophysical Journal Letters. The team studied images taken by the Hubble Space Telescope from 1994 to 2014, and spectra from the Very Large Telescope spanning 2000 to 2013. Based on the rate at which the hotspots are fading, the researchers predict the glittering necklace will fade away sometime between 2020 and 2030, with the calculations favoring closer to 2020. The clumps of gas in the central ring are likely dissolving, thanks to a combination of instabilities and conduction in the hot gas surrounding the clumps. In other words, the central ring is being destroyed.

The show really isn’t over. The aftermath of a star exploding goes on for thousands of years. So to will SN1987a’s show.

Hubble finds something astronomers can’t explain

The uncertainty of science: The Hubble Space Telescope has spotted the explosion of a star that does not fit into any theory for stellar evolution.

The exploding star, which was seen in the constellation Eridanus, faded over two weeks — much too rapidly to qualify as a supernova. The outburst was also about ten times fainter than most supernovae, explosions that destroy some or all of a star. But it was about 100 times brighter than an ordinary nova, which is a type of surface explosion that leaves a star intact. “The combination of properties is puzzling,” says Mario Livio, an astrophysicist at the Space Telescope Science Institute in Baltimore, Maryland. “I thought about a number of possibilities, but each of them fails” to account for all characteristics of the outburst, he adds.

We can put this discovery on the bottom of a very long list of similar discoveries by Hubble, which this week is celebrating the 25th anniversary of its launch.

On that note, as part of that celebration today has published a long interview with me about Hubble and my book, The Universe in a Mirror, the saga of the Hubble Space Telescope and the visionaries who built it. They have also published an excerpt from the book. Check both out.

For more information about that newly discovered supernova in the nearby galaxy M82 go here and here.

For more information about that newly discovered supernova in the nearby galaxy M82 go here and here.

The first link notes that the supernova has brightened to 11.5 magnitude and could get even brighter in the next two weeks. Though still too dim for the naked eye, it is easily bright enough right now for most amateur telescopes and binoculars. How much brighter it will get remains a question.

Astronomers have identified a star they expect to go supernova very soon.

Astronomers have identified a star they expect to go supernova very soon.

[SBW2007] 1 (or SBW1) is located 20,000 light-years from Earth and features an enigmatic double-ringed planetary nebula. The rings are gases that have been blasted from the outermost layers of the blue supergiant star in the nebula’s core. The star, which was estimated to be 20 times the mass of the sun before it became unstable, is going through its final death throes before a supernova is initiated. But don’t worry, the supernova would be a safe distance from us, although it will put on an exciting light show.

There is no way to predict when the supernova will occur. On the timescales of stellar evolution, it could happen tomorrow, or in a thousand years. For the full Hubble image go here.

This story is significant in that it shows how much knowledge has been gained in astronomy since Hubble’s launch. In 1987, when Supernova 1987a exploded in the Large Magellanic Cloud, astronomers had not identified even one progenitor of any supernova, and did not have any clear idea what kinds of stars produced these gigantic explosions. Today, they have identified more than a handful, and are even beginning to pinpoint candidates, such as the star above, that could be the next stars to go boom.

The remarkable remains of a most recent supernova.

The remarkable remains of a most recent supernova.

Astronomers estimate that a star explodes as a supernova in our Galaxy, on average, about twice per century. In 2008, a team of scientists announced they discovered the remains of a supernova that is the most recent, in Earth’s time frame, known to have occurred in the Milky Way. The explosion would have been visible from Earth a little more than a hundred years ago if it had not been heavily obscured by dust and gas. Its likely location is about 28,000 light years from Earth near the center of the Milky Way.

A star has gone supernova and astronomers get to see it from the very beginning, and even earlier!

A star has gone supernova and astronomers get to see it from the very beginning, and even earlier!

The star had erupted several times before but had not produced a real supernova explosion. On September 26 it finally did so. Moreover, astronomers have images of the star prior to any eruption, information that until recently was not available for any supernovae.

Have astronomers found a future supernova?

A press release from the Carnegie Institute today described a recent paper by astronomers that might have identified a star in the Milky Way that might go supernova sometime in the future. The star QU Carinae, is a cataclysmic variable, a binary system in which material dumped from one star onto another periodically causes an outburst of X-rays.

I emailed Stella Kafka, the lead scientist of the research paper, to find out how far away QU Carinae is and how soon it might go supernova. She responded as follows:
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A supernova twenty-five years later.

A supernova twenty-five years later.

SN 1987A, it turns out, was like a dust-bomb, with estimates of the total dust it threw into space, based on the infrared brightness of the dust … implying enough dusty material to build the equivalent of 200,000 Earth-mass planets. Mingled within the dust are elements as diverse as oxygen, nitrogen, sulphur, silicon, carbon and iron. This immense amount of dust has been beyond expectations and, if all supernovae spew out this much dust, it helps explain why young galaxies that we can see existing in the early Universe, which have high rates or star birth and death, are so dusty. The dust, however, isn’t a nuisance to be wiped away – this is the material that goes into building new planets, moons and even life. The iron in your blood and the calcium in your bones all came from supernovae like SN 1987A, as mostly did the oxygen we breath and the carbon in our constituent molecules.

The last remant of a supernova

Time for some astronomical sightseeing! This image, produced from data taken by both the Hubble Space Telescope and the Chandra X-ray Observatory, shows what astronomers call a supernova remnant. The bubble, located in the Large Magellanic Cloud 160 thousand light years away, is thought to be 23 light years across and expanding about 11 million miles per hour. It is thought that the supernova itself took place around 1600. That we have no record of it is probably because it was only visible in the southern hemisphere, where few records of such events were being kept at that time. More here, including the image using only Hubble data as well as a video animation that is quite stunning.

Supernova remnant