This beautifully bright cosmic debris of a star that died 4,800 years ago is arguably one of the Cloud’s most fabulous objects to observe! N49 is the LMC’s brightest supernova remnant (and along with N63A, and N132D the first extragalactic SNRs discovered). It is 75 light-years in size, and its unique filamentary structure has long set N49 apart from other well understood SNRs, as most appear roughly circular in visible light. This supernova explosion is unexpectedly lopsided and its remnant is expanding into a denser region to the southeast, which causes its asymmetrical appearance. Astronomers say that N49 is almost certainly the result of a type II explosion.

There is a lot to ponder when one explores this tiny beauty for at its heart it harbours a rare and mysterious class of star whose discovery was brought about by the famous “March 5th Event” …

… On March 5, 1979, at approximately 14:51 UTC, a pulse of gamma rays that was 100 times brighter than any gamma ray burst yet seen, blazed across the Solar System. The burst only lasted 0.02 of a second, but an event somewhere out in the Universe had unleashed as much energy in a mere fraction of a second as the Sun will radiate in 10,000 years of its life.

First hit with the blast of gamma radiation were two Soviet spacecraft, Venera 11 and Venera 12, which were in heliocentric orbit (they had just dropped probes off at Venus). Eleven seconds later NASA’s Helios 2 space probe that was orbiting the Sun, was saturated by gamma radiation. Venus was next in line, with its Pioneer Venus Orbiter’s detectors registering the blast. Then it was Earth’s turn and three Vela Satellites (operated by the US Dept. of Defence), the Soviet Prognoz 7, and the Einstein Observatory all registered the wave of high energy radiation. And finally, just before it left the Solar System, the wave passed over the International Sun-Earth Explorer in distant halo orbit.

This was the first time an enormous swell of energy was detected travelling as a wave across the Solar System. Having the massive surge recorded by the instruments of 10 spacecraft made it possible for scientists to do some clever detective work and figure out that the source of the high-energy wave originated in the supernova remnant N49 in the Large Magellanic Cloud.  (A series of lower energy gamma rays and x-rays arrived over the course of 200 seconds, repeating every 8 seconds. Half a day later, another small burst of high energy radiation arrived.)

The source of the “March 5th Event” is now attributed to a magnetar. The existence of magnetars was proposed in 1992 by U.S. astrophysicists Robert Duncan and Christopher Thompson. A magnetar (a contraction of magnetic star) is a neutron star with an outlandishly intense magnetic field. At ~1015 gauss, the magnetic field is a quadrillion (thousand trillion) times stronger than the Earth’s, and between 100 and 1,000 times stronger than that of a radio pulsar, making them the most magnetic objects known. The magnetar in N49 has had several subsequent gamma-ray emissions and is now recognized as a “soft gamma-ray repeater” (thus named SGR 0526-66), a distinct class of objects that are recurrent, and not one-off events like gamma ray bursts.

X-ray: (NASA/CXC/Penn State/S.Park et al.); Optical: NASA/STScI/UIUC/Y.H.Chu & R.Williams et al

Magnetar bGR 0526-66 lies far away from the centre of the supernova remnant; it is hurtling through the supernova debris at over 1,200 kilometres per second. In the gorgeous, composited image based on data from the Chandra and Hubble Space Telescopes, the point source is magnetar SGR 0526-66 that was kicked out from the centre of the supernova explosion. The blue cosmic bullet rocketing away from the magnetar at 8 million kph was ejected from the huge star’s explosion.

Adding to the remnant’s intrigue is its asymmetry. Pinning down why and how the occasional stellar remnant gets so messy will help astronomers understand stellar life cycles more completely.

As an interesting aside, N49 and the March 5th Event is mentioned in Chapter 9 of Carl Sagan’s book Cosmos, where he also notes that by accident it was also the date that Voyager 1 encountered the Jupiter system.

Even without a filter with the 16″ at 90x the SNR is visible as a faint, small, strangely triangular-shaped glow, its flanks distinct and well-defined. I am not sure this isn’t my favourite view of this bright little SNR for it appears as exactly what it is… a pale little star-ghost lying amongst its sparkling brethren. The contrast with the UHC filter is tremendous, and at 130x it’s a splendid sight! A bright little scrap of condensed looking light that is somewhat dimmer in the centre. Its peculiar shape – almost like a triangle with a rounded apex (the apex to the east) – is apparent and its edges are well defined, except to the north where it appears fuzzy and diffuse. At 228x with the filter, the SNR is beautiful! It’s a bright and beautiful silky glow, and its darker central part is more apparent. I can see what looks like a darker indentation on its west side. Averted vision reveals the faintest mottling effect to the southeast. The northern edge appears even more diffuse and fuzzy, while the rest of its edges are crisp. Without the filter, a faint star hovers close to its northern edge.

What a superb beauty this little SNR is!