From Ethan Siegel: “Closest Supernova In Years Brings Cosmic Fireworks To Earth’s Skies”

Ethan Siegel
May 17, 2017

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Patrick Wiggins
The discoverer of this supernova, Patrick Wiggins, took these two images of the Fireworks galaxy on May 12th and May 14th, with the additional light in the more recent image showing the location of the night sky’s newest supernova.

After burning bright for millions of years, the brightest stars of all are destined to explode in one final blaze of glory: a supernova.

Supernova remnant Crab nebula. NASA/ESA Hubble

Capable of shining as bright as many billions of stars put together, the light from a single outburst can be seen with the naked eye if it occurs in our own galaxy, and through a modest telescope from even tens of millions of light years away. On May 14th, a brand new supernova was discovered just 22 million light years away in a prolific object known as the Fireworks galaxy, making it the closest supernova to grace the skies in three years.

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Fireworks galaxy. NASA

With warm weather and summer approaching, this is the best chance you’ll likely have to see one for yourself all year.

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This image of the center of NGC 6946, constructed from multiple Hubble instruments, filters and observations, showcases the dusty arms present around the galactic core. This galaxy is a hotbed of new star formation. ESA/Hubble and NASA / Judy Schmidt

When a star is born, it’s destined to shine brightly under the power of its own internal, nuclear reaction for anywhere from millions to trillions of years. But the most massive stars have a uniquely spectacular fate in store as their destiny: after burning through all the fusible material in its central region, its core will collapse under its own gravity. With radiation and even the pressure of the atoms and atomic nuclei themselves unable to resist the intense forces at play, the core implodes, triggering a runaway fusion reaction. The result is a Type II supernova explosion, which occurs only once per century in a galaxy like the Milky Way.

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Cas A Type II Supernova Remnant. NASA Chandra

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Two images of NGC 6946: one from 2011 and a similar one from May 14, 2017, which shows the new and brightening supernova, SN 2017eaw. Gianluca Masi / Virtual Telescope Project / Tenagra Observatories, Ltd

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Tenagra Observatories, Ltd, Rio Rico, Arizona, USA

But in a nearby spiral galaxy that has only half the stars of our Milky Way, these cosmic fireworks occur ten times as frequently. In fact, the galaxy in question, NGC 6946, is nicknamed the Fireworks galaxy [above]for exactly this reason. Located just 22 million light years away, on the border of the constellations Cygnus and Cepheus, an amateur astronomer named Patrick Wiggins discovered a new point of light on May 14th where none had been seen previously, including just two days prior, on May 12th.

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This side-by-side image shows a ground-based view of the relevant region of the Fireworks galaxy (L), along with that same region as imaged with Hubble data years ago (R). The progenitor star can clearly be identified, suggesting a massive, core-collapse supernova as the origin of this new light. Las Cumbres Observatory (L); ESA/Hubble and NASA (R)

NASA/ESA Hubble Telescope

Follow-up observations confirmed that this is, in fact, a Type II supernova, one that continues to brighten as the days pass by. This very region of the galaxy happened to be previously imaged by the Hubble Space Telescope, which confirms that there was a progenitor star there, faint but clearly visible, despite the incredible cosmic distance separating us. It’s a spectacular find, and one you can see with yourself through a backyard telescope, so long as you know where to look.

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The brightest star in Cepheus, Alderamin, is relatively close to the Fireworks galaxy. By tracing an imaginary line back towards Vega, you can arrive at NGC 6946’s approximate location. E. Siegel / Stellarium

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The bright stars Vega and Deneb make up two-thirds of the Summer Triangle, which begins rising in the northeast skies after sunset as summer approaches. Moving away from Deneb in the east and heading towards Polaris, the north star, you’ll encounter the brightest star in Cepheus: Alderamin. If you then trace an imaginary line back towards Vega, the unmistakably bright, blue star you started at back at the beginning, and move about the width of three fingers held at arm’s length, you’ll want to point your telescope there.

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The galaxy NGC 6946, supernova SN 2017eaw (denoted with red markings) and the open star cluster NGC 6939. Although the galaxy and the cluster take up the same approximate area on the sky, the galaxy is 22 million light years away, while the star cluster is within our own galaxy at a mere 3860 light years distant. Gianluca Masi / virtualtelescope.eu

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virtualtelescope.eu, Bellatrix Astronomical Observatory, Italy

A bright star cluster, NGC 6939 (top right, above) and a faint galaxy, NGC 6946 (lower left, above) should appear in the same frame. If you can see the bright “star” located at about the 1 o’clock position of the Fireworks galaxy, that’s no star at all; that’s the latest firework! What you’re seeing is the tenth supernova discovered in the Fireworks galaxy since 1917, where the first one was discovered exactly 100 years ago. No other galaxy has had as many supernovae over this period, which might surprise you, considering that it’s less than a third the extent of the Milky Way.

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This infrared observation of the Fireworks galaxy from NASA’s Spitzer space telescope showcases the warm gas that will become a part of the next generation of stars yet to form in NGC 6946. NASA / JPL-Caltech / SSC / R. Kennicutt et al.

NASA/Spitzer Telescope

Size isn’t everything, though! The key to a supernova factory is to have formed a large number of massive stars very recently. In almost every case, the place to look for that is inside an incredibly large star-forming region. When giant clouds of molecular gas collapse, triggered by a supernova, collision, or a major gravitational merger, large amounts of stars form. If the region is massive enough, a huge number of high-mass stars form as well. In the case of this galaxy, practically the entire thing has become a star-forming region.

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The unmistakable pink color along the spiral arms traces out regions of ionized hydrogen, caused by the formation of hot, young stars in this galaxy, many of which will eventually go supernova. AURA/Gemini Observatory

Gemini/North telescope at Mauna Kea, Hawaii, USA


Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile

Galaxies exhibiting a huge rate of star formation throughout are known as starburst galaxies, and are usually triggered by a major merger or galactic interaction. The pink regions seen throughout, above, are indicative of new and current star formation, and help explain why Type II supernovae are so common in this galaxy. With 10 supernovae in the past century, including four already in the new millennium, you’d expect to see a large number of X-ray sources as a result of these cosmic fireworks.

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This X-ray image of the Fireworks galaxy reveals a barred spiral structure, extended regions of intense star formation, and a large number of X-ray point sources, indicative of supernovae that occurred millions of years in the past but whose light is just reaching us now. NASA/CXC/MSSL/R.Soria et al.

NASA/Chandra Telescope

Even from 22 million light years away, the Chandra X-ray observatory can see exactly that. The gas within the spiral arms is heated to such a degree that there’s a diffuse glow extending throughout the star-forming portion, but it’s the bright point sources that are most interesting. Representing both active black holes and recent supernova remnants, this data revealed three of the oldest supernovas ever detected in X-rays. When you combine the optical and X-ray images, you can see just what makes this galaxy so spectacular.

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A composite of X-ray (Chandra, above) and optical (Gemini, above) data show the extent of the star forming regions of the Fireworks galaxy, NGC 6946. X-ray: NASA/CXC/MSSL/R.Soria et al, Optical: AURA/Gemini OBs

Cosmic fireworks like these don’t truly happen at random; they are clustered in time and space around the most massive, intense star-forming regions of all. You can’t have a bigger star-forming region than one that includes the entire galaxy, and the sweeping, grand, irregular arms of the Fireworks galaxy are as good as they come. Based on what we see, we expect this elevated rate to continue for more than a million years. Keep an eye on this galaxy for the appearance of a “new star,” and if you find one, you just might discover the Universe’s newest supernova!

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“Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

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