Ancient Supernova Ripple Discovered Near The Big Dipper

The Ursa Major Arc is about 600 light years away and encircles the Big Dipper (part of Ursa Major the Great Bear), and portions of the Little Dipper, Draco and Canes Venatici. The faint arc requires high-end cameras and a special filter that blocks all visible light except the light of glowing hydrogen. Stellarium map with additions by Bob King; source: Robert Benjamin. CC-BY-SA-3.0 

Drop a stone in a pond and ripples spread into every widening circles. Blow up a star and its blast wave sweeps up and excites thinly strewn atoms to form an ever-expanding glowing circle in space. A team of astronomers stumbled on just such a ring about 600 light years away that spills into four different constellations including the familiar Big and Little Dippers.

The 30° arc of compressed hydrogen gas is extremely faint so you’ll have to use your imagination to picture it curving between the two dippers. Andrea Bracco of the University of Paris and her team discovered it by chance while examining images taken by NASA’s Galaxy Evolution Explorer (GALEX), an orbiting telescope that photographed the sky in ultraviolet light from 2003 until early 2012. While examining what appeared to be a linear filament of gas they noticed it was actually slightly curved. The “line” proved to be only a short segment of a much larger arc.

This is a view of the Ursa Major Arc taken during the MDW Survey. The narrow arc is formed from a mix of supernova ejecta and gases in space swept up by the blast wave from a supernova (or nova) and compressed to glow. See more spectacular images of the sky in hydrogen light including one of the constellation Orion at the MDW Sky Survey website. David Mittelman, Dennis di Cicco & Sean Walker

Dubbed the Ursa Major Arc it appears to be an expanding shock wave originating in a supernova (or possibly nova) explosion that occurred about 100,000 years ago. Astronomers have photographed similar arcs and filaments that form in the wake of supernovae explosions called supernova remnants. One of the most famous is the Crab Nebula in Taurus. While the new discovery is much too faint to see visually in a telescope it takes the cake for size — if you complete the arc it extends across 48° of sky!

The Crab Nebula, so called because its tendrils reminded an early observer of a crab’s legs, was spawned by a supernova in the year 1054 A.D. NASA / ESA

100,000 years ago early humans (us) emerged in Africa and soon migrated into Europe and Asia. One wonders whether our ancestors may have seen the original supernova blast and stopped to look, wonderstruck. Would it have resembled the explosion in 1054 that birthed the Crab Nebula? Chinese astronomers recorded a brand new  “star” in Taurus in July that year brighter than Venus. Anyone with a modest telescope can see the explosion’s expanding remains today. Would that the Ursa Major remnant were as bright, but it occurred so long ago it has since faded.

You don’t need a satellite to photograph it however. Amateur astronomers David Mittelman, Dennis di Cicco, and Sean Walker have been working on a project called the MDW Survey to photograph the entire sky in the light of glowing hydrogen gas called “hydrogen alpha (H-alpha)” light using a special “narrow band” filter. Stellar birth clouds called nebulas are rich in hydrogen which fluoresces a beautiful pink when ultraviolet light from massive, newborn stars excites the gas. Their photos show an extremely narrow circular arc that lines up neatly with the same arc seen in the GALEX ultraviolet images.

This is the eastern half of the Veil Nebula in Cygnus, a supernova remnant like the Ursa Major Arc that was created by a massive stellar explosion that occurred 5,000 to 8,000 years ago 1,500 light years away. David Chifiriuc, CC-BY-SA 4.0

Diagrams and photos show the arc — part of a circle — in two dimensions. To really picture what hovers near the Big Dipper we must imagine the blast wave as an expanding sphere in three dimensions. A gigantic, continuously-inflating bubble. The arc we see defines the edge of that bubble while the center — invisible thus far in any photos — bulges toward us and the even more distant while backside bows away.

Supernova blast waves have a side benefit. They sweep away the dust and gas scattered across space like a brisk wind, clearing the view into the great beyond where we might discover the faintest and most remote galaxies.

Visible or not, the enormity of this supernova fossil is a feast for the imagination.

5 Responses

  1. Brian Rajala

    I have it been able to communicate on your site for a couple years? The email address I have used for years has not been working and I have not been able to get in on with a different address.

    I wanted to hear your opinion on this?


    Phil Plait
    Jul 01, 2020
    Astronomers have found the most massive known black hole in the very early Universe, and it’s a whopper: It has 34 billion — yes, billion, with a b — times the mass of the Sun.

    And that’s only one part of this story that has the hair on the back of my neck standing up. Stick around for the rest. I promise, it’s hair-stand-uppable.

    A binary pair of black holes about to merge together, near the huge disk of material swirling around a supermassive black hole in a distant active galaxy. Credit: Caltech/R. Hurt (IPAC)
    Merging black holes blast out light… but not for the reason you’d think
    Pick a date, any date. The answer is still “nope.” Credit: Dean Reeves, used by permission
    No, the Maya did not predict the end of the world on 21 June 2020
    The black hole is in the center of an active galaxy called a quasar. These are where the central supermassive black hole (which every big galaxy has) is actively eating material. This stuff piles up into a disk around the black hole, swirling madly around it. Matter that’s closer in moves very near the speed of light, and stuff farther out is slower, and as they rub together they generate friction, which heats the disk up a lot (imagine rubbing your hands together at the speed of light to see why). The temperature is so high, and there’s so much matter in the disk, that it glows incredibly brightly, in general outshining all the stars in the galaxy combined.

    The quasar in question is called SMSS J215728.21–360215.1. Let’s call it J2157 for short. The astronomers found it looking at sky surveys for objects with the right colors to be very very far away active galaxies, and this one was found in the SkyMapper Southern Survey (hence the SMSS in the name; the rest is for its coordinates on the sky).

    The quasar SMSS J215728.21–360215.1 hosts the most massive black hole known in the very early Universe. It may not look like much, but it’s 12.5 billion light years away, and blasts out energy a thousand times our entire galaxy. Credit: DSS2 / Aladin

    Once they determined it was likely to be a distant quasar, they observed it with the monster 10-meter Keck telescope in Hawaii and the 8-meter Very Large Telescope in Chile. By breaking the light up this way a lot of important information can be found, including how far away the quasar is, how bright it is overall, how massive that black hole is, and how much matter falls into it from the disk.

    The quasar is crushingly far away: The light we see from it left it more than 12.5 billion years ago, just 1.25 billion years after the Big Bang itself. So we see this quasar as it was when it was very young.

    The mass of the black hole is 34±6 billion times the mass of the Sun. For comparison, the supermassive black hole in the center of the Milky Way is about 4 million solar masses, so the one anchoring J2157 is over 8,000 times as massive.


    There are whole galaxies with less mass than just this one black hole. It’s so big that if you replaced the Sun with it, it would encompass the entire solar system — it’s roughly 200 billion kilometers across. That’s… huge.

    Artwork depicting a black hole with an accretion disk, and magnetic fields swirling above it. Credit: NASA/JPL-Caltech

    I’ll note that several more massive black holes have been found, but these are in galaxies closer to us than J2157. This one, though, is the most massive ever found at this distance range from us, at this early of a period in the Universe.

    But we’re not done! Measuring the brightness of the object and knowing its distance allows the total energy emitted by the quasar to be found. It’s 1.6 x 1041 Joules/second. Are you sitting down for this next bit? That is one quadrillion times the amount of light the Sun emits.

    One quadrillion. 1,000,000,000,000,000. Our entire Milky Way galaxy emits a fraction of a percent that much light. This makes J2157 the most luminous known quasar.

    The physics is a bit complicated, but it’s also possible to estimate out how much matter is falling into the black hole to generate that much energy: It turns out to be about the mass of the Sun every day.

    I ran the numbers and got the same answer. Even so it’s hard to grasp. In more local terms, that black hole is gobbling down the equivalent of the mass of the Earth four times per second.

    Wow. Imagine tossing planets into a black hole that rapidly. That’s hundreds of thousands of times per day. Or, if you prefer, a hundred million times per year.

    So, how’s that neck hair? Piloerected yet?

    Everything about this object is overwhelming. But there’s real scientific value here. This being the biggest known black hole at this early an age in the Universe is a solid constraint on our understanding of how they grow. Did it get to this size by starting off big and eating rapidly, or starting off smaller and eating really rapidly? Did a bunch of smaller black holes form together and then merge to make its rapid growth? Is there some other weird thing going on here we haven’t thought of yet?

    We know that the amount of light emitted by the disk increases with the mass of the black hole, and this one seems to fit that pattern. That means as weird as it is, it’s normal compared to other supermassive black holes, except for being even more supermassiver. That’s oddly reassuring, assuming you’re comfortable with supermassive black holes in the first place.

    At this distance, it’s also telling us about conditions in the very early Universe, when galaxies were first getting started. We still don’t know a whole lot about this era, and every example we get is a piece of that puzzle we can examine.

    In this case, a ridiculously massive, bright, and vastly gluttonous one.

    1. astrobob

      Hi Brian,
      I find it amazing. That’s one big and hungry black hole. There’s no end to discovery, and that’s why I love science.

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