There has been a lot of hype in the press about T Coronae Borealis (T CrB), the so-called Blaze Star and a once-in-a-lifetime event. But what is it, when will it blaze and can I see it?

Personally, I think it’s important to temper expectations as this will not appear to be a very dramatic event, but if you use your imagination a little and visualise the processes going on in this system then it really is amazing! Read on…

What is it?

White dwarf pulling material away from a red giant

Artist’s impression Credit: NASA/CXC/M.Weiss

T CrB is a recurring nova, a star that explodes in such a way that it dramatically increases in brightness but does not actually destroy itself (unlike a supernova) and so can happen again – in the case of T CrB every 80 years or so. T CrB is actually a binary star system about 3,000 light years away, with the two stars rotating around each other every 227 days. A small planet-size White Dwarf star pulls matter from a Red Giant into a rotating disk around itself. The cause of the outbursts is a massive dumping of matter onto the White Dwarf from the disk causing a thermo-nuclear explosion.

When will it blaze?

We really don’t know, but it has been observed to outburst several times in the past, in 1787, 1866 and 1946 as well as possibly 1217. The pattern of brightness fluctuations that we are seeing now, similar to those seen in the past, makes astronomers believe it is due to have another outburst anytime now. But as with all investments, “past performance is no guarantee of future results”. We have far more comprehensive and accurate data now than we had during the last outburst 80 years ago, so we really don’t know – but are very hopeful.

Once-in-a-lifetime? Well maybe, but other novae do happen occasionally and this one, although perhaps different because it is more predictable and possibly brighter than most, may not be any more spectacular.

Can I see it?

Yes you will be able to see it, Scottish weather-permitting that is, but be warned it won’t look as dramatic as the hype might suggest. Basically, there will be another naked eye visible star – a “new star” (nova) – in the constellation of Corona Borealis where there wasn’t one before. It will be as bright as the current brightest star in the constellation, Alphecca, similar to the brightness of the Pole Star, but it will start to fade almost immediately, becoming invisible to the naked eye maybe 5 days later. A second outburst is expected about 85 days after the first, but you’ll need a small telescope or binoculars to see that.

Corona Borealis is not one of the more prominent or well-known constellations so you would be forgiven for overlooking it. The Northern Crown is like a bowl of stars as you can see in the finder chart at the top of this article. However, there are other signposts in the sky that you might be able to find to help you locate this constellation.

The chart above shows the night sky in Scotland for midnight in the middle of the month looking south. The well-known summer triangle, made up of the 3 bright stars Vega in Lyra, Deneb in Cygnus and Altair in Aquila, rides high just east of south. The less well-known  and fainter “keystone” in Hercules lies just west of south, with the bright star Arcturus in Boötes further west. Corona Borealis can be found between the keystone and Arcturus. Binoculars might help.

The Blaze Star

So it may not be the most spectacular looking event in the night sky but when you consider what is going on, the massive processes causing the blaze, it really is amazing!

But there are many more equally fascinating objects in our night sky and we hear about these in our regular talks. You can see some of these on our YouTube channel or join us at a future event. Visitors are always welcome!

The Astronomical Society of Edinburgh have been observing T CrB over the past few months using our remote observatory in Spain, ASERO.

Mark Phillips

Chart created using Cartes du Ciel