N49, an asymmetric supernova remnant in the LMC

N49, an asymmetric supernova remnant in the LMC

N49 (also designated LMC N 49 or DEM L 190) is a supernova remnant of about 75 light-years across, located within the Large Magellanic Cloud (LMC), some 160,000 light-years away in the southern constellation Dorado. N49 is the brightest supernova remnant in the Large Magellanic Cloud. It has million-degree gas in its center but cooler gas at the outer parts, between 8,000 and 300,000 degrees.

The supernova remnant N 49 is only a few thousand years old. However, because of its distance, it takes the light of the stellar explosion 160,000 years to reach Earth. So, by our Earth calendars the blast actually occurred over 160,000 years ago.

A massive dying star produced a strong wind that cleared a low density bubble around it. When the star exhausted its supply of hydrogen, it exploded, sending a shock wave through the interstellar gas. The shock wave has now encountered the shell of dense gas at the edge of the bubble, what slows the shock wave to 100 – 300 kilometers per second.

The core of the original star, which lies deep within this cloud of gases, is a neutron star that is spinning at the blinding speed of one revolution every eight seconds. Its magnetic field is about a quadrillion (a thousand times a trillion) times more powerful than that of the Earth, putting it in the rare category of “magnetars”. This magnetar hurtles through the supernova debris cloud at over 1,200 kilometers per second.

On March 5, 1979, this magnetar displayed a historic gamma-ray burst episode. Gamma rays have a million or more times the energy of visible light photons. The neutron star in N 49 has had several subsequent gamma-ray emissions, and is now recognized as a “soft gamma-ray repeater.” These objects are a peculiar class of stars producing gamma rays that are less energetic than those emitted by most gamma-ray bursters.

The neutron star in N 49 is also emitting X-rays, whose energies are slightly less than that of soft gamma rays. High-resolution X-ray satellites have resolved a point source near the center of N 49, the likely X-ray counterpart of the soft gamma-ray repeater.

The delicate filaments and knots throughout the supernova remnant — also visible in X-ray — are sheets of debris from the stellar explosion. This filamentary material will eventually be recycled into building new generations of stars in the Large Magellanic Cloud. Our own Sun and planets are constructed from similar debris of supernovae that exploded in the Milky Way billions of years ago.

The unique filamentary structure has long set N49 apart from other well understood supernova remnants, as most supernova remnants appear roughly circular in visible light. This supernova remnant is expanding into a denser region to the southeast, which causes its asymmetrical appearance.

This image is a color representation of data taken in July 2000, with Hubble’s Wide Field Planetary Camera 2. Color filters were used to sample light emitted by sulphur, oxygen and hydrogen.

Image Credit: Hubble Heritage Team (STScI / AURA), Y. Chu (UIUC) et al., NASA

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