Anne’s Picture of the Day: The Great Barred Spiral Galaxy

read more at Anne’s Astronomy News http://annesastronomynews.com/

March 11, 2013

The Great Barred Spiral Galaxy in Fornax

Image Credit & Copyright: Martin Pugh Astrophotography (http://www.martinpughastrophotography.id.au/)

NGC 1365, also known as the Great Barred Spiral Galaxy, is, as you would have guessed by its nickname, a huge barred spiral galaxy. It is over 200,000 light-years across, what makes it one of the largest galaxies known, and lies about 56 million light-years from Earth in the constellation of Fornax, while it is receding from us at approximately 1636 kilometers per second. It is a major member of the Fornax cluster which consists of 58 galaxies.

The galaxy has a straight east-west bar and two very prominent outer spiral arms that extend in a wide curve north and south from the ends of the bar and form an almost ring like Z-shaped halo. Closer to the oval-shaped center is a second spiral structure and the young luminous hot stars, born out of the interstellar clouds, give these arms a prominent appearance and a blue color. The whole galaxy is laced with delicate dust lanes.

This image reveals very clearly the glow from vast numbers of stars in both the bar and the spiral arms. The huge bar disturbs the shape of the gravitational field of the galaxy and this leads to regions where gas is compressed and star formation is triggered.

Many huge young star clusters trace out the main spiral arms and each contains hundreds or thousands of bright young stars that are less than ten million years old. NGC 1365 is too remote for single stars to be seen in this image and most of the tiny clumps visible in the picture are really star clusters. Over the whole galaxy, stars are forming at a rate of about three times the mass of our Sun per year.

While the bar of the galaxy consists mainly of older stars, many new stars are born in stellar nurseries of gas and dust in the inner spiral close to the nucleus. The bar also funnels gas and dust gravitationally into the very center of the galaxy, where a supermassive black hole is hidden among myriads of bright new stars.

This black hole has a mass 2 million times that of our Sun and is spinning almost as fast as Einstein’s theory of gravity will allow. Supermassive black holes are surrounded by pancake-like accretion disks, formed as their gravity pulls matter inward. The bright center of NGC 1365 is thought to be due to huge amounts of superhot gas ejected from such an accretion disk circling this central black hole.

The bar rotates clockwise with velocities in the nucleus of 2000 kilometers per second resulting in one rotation in 350 million years.

Supernovae 1957C, 1983V, 2001du and 2012fr (discovered on 27 Oct 2012) were observed in this galaxy.

n/a