4 Unusual Mysteries surrounding Fireworks Galaxy, NGC 6946

NGC 6946 is a medium-sized, face-on spiral galaxy about 22 million light years away from Earth. In the past century, eight supernovas have been observed to explode in the arms of this galaxy. Chandra observations (purple) have, in fact, revealed three of the oldest supernovas ever detected in X-rays, giving more credence to its nickname of the "Fireworks Galaxy." This composite image also includes optical data from the Gemini Observatory in red, yellow, and cyan. Image credit: X-ray: NASA/CXC/MSSL/R.Soria et al, Optical: AURA/Gemini OBs

NGC 6946 is a face-on typical spiral galaxy with a tiny bright nucleus whose position in the sky rides the boundary between Cygnus and Cepheus’s northern constellations. Its distance from Earth is about 7.72 megaparsec or 25.2 million light-years, similar to M101 (NGC 5457) in the constellation Ursa Major.

What’s unusual about NGC 6946? Pretty much everything.

This visible-light image of the Fireworks galaxy (NGC 6946) comes from the Digital Sky Survey, and is overlaid with data from NASA’s NuSTAR observatory (in blue and green). Credit: NASA/JPL-Caltech

Let’s find out 4 unusual things scientists noticed while observing NGV 6946.

  1. Red Eclipse: Various exotic celestial objects have been seen within NGC 6964. ‘Red Ellipse’ is one of them. It is located around one of the northern arms that looks like a super-bubble or massive supernova remnant, and which may have been formed by an open cluster comprising massive stars. However, the gigantic size, and particularly the spectroscopic data obtained recently with the Special Astrophysical Observatory, made scientists believe that this object could not be a supernova remnant.
  2. Darkness: There are two regions of prominent dark lanes of nebulosity. Several areas appear devoid of stars and gaseous hydrogen within the spiral arms, crossing up to two kiloparsecs. Scientists have found no explanation for these features.
  3. Fireworks Galaxy: Ten supernovae have been recorded in NGC 6946 in the last century: SN 1917A, SN 1939C, SN 1948B, SN 1968D, SN 1969P, SN 1980K, SN 2002hh, SN 2004et, SN 2008S, and SN 2017eaw. For this reason, NGC 6946 was dubbed the “Fireworks Galaxy,” a name growing increasingly popular. NGC 6946 has an extraordinarily high supernovae production rate compared to our Milky Way galaxy, whose rate averages just one supernova event per century. This is more unusual as our Galaxy contains twice as many stars.
  4. X-Ray Mystery: Flashes of bright green and blue in the image above the NGC 6946 shows the areas of bright sources of X-ray light captured by NASA’s NuSTAR space observatory. Created by some of the most energetic rules in the universe, these X-ray sources are rare than the many visible light sources in the image. The new research explores the probability that the light came from a black hole absorbing another object, perhaps as a star. If any celestial body gets too close to a black hole, gravity can uproot that object apart, bringing the debris into a tight orbit around the black hole. The material at the inner edge of this newly formed disk starts moving so fast that it heats up to billions of degrees and emits X-rays. Hot!

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