Starship Asterisk*

For some reason, I hadn't seen this post before. How very very interesting! And what an amazing galaxy NGC 6984 is! Just look at that "bottom arm" of the galaxy: how incredibly thick, bright and blue it is!!! Even though I'm not sure, I believe that NGC 6984 may be even bluer than M101, which is the bluest of all large nearby galaxies. NGC 6984, like M101, might be a really big and bright galaxy, too. This too makes NGC 6984 unusual, since very blue galaxies are usually small and irregular. According to Principal Galaxy Catalog (PGC), the B-V index of NGC 6984 is 0.440 and its U-B index is -0.170. Both values are really quite blue. But according to PGC, NGC 6984 is also 2.4 times as bright as the Milky Way, and for a very blue galaxy, such a high luminosity is indeed very unusual.

So in view of the fact that this galaxy is bursting with massive young stars, it is not surprising that two of them have collapsed under their own weight and blown their tops quite recently![img]http://www.bdoutdoors.com/forums/images/smilies/Exploding_Smiley.gif[/img][img]http://www.bdoutdoors.com/forums/images/smilies/Exploding_Smiley.gif[/img]

Ann

[url=http://www.spacetelescope.org/images/potw1344a/][size=120][b][i]Stellar explosions in NGC 6984[/i][/b][/size][/url]
ESA/HEIC Hubble Picture of the Week | 2013 Nov 04
[quote]
[float=right][img3=""]http://www.spacetelescope.org/static/archives/images/screen/potw1344a.jpg[/img3][/float]Supernovae are intensely bright objects. They are formed when a star reaches the end of its life with a dramatic explosion, expelling most of its material out into space. The subject of this new Hubble image, spiral galaxy [url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=NGC+6984]NGC 6984[/url], played host to one of these explosions back in 2012, known as [url=http://www.rochesterastronomy.org/sn2012/index.html#2012im]SN 2012im[/url]. Now, another star has exploded, forming supernova [url=http://www.rochesterastronomy.org/sn2013/index.html#2013ek]SN 2013ek[/url] — visible in this image as the prominent, star-like bright object just slightly above and to the right of the galaxy's centre.

SN 2012im is known as a Type Ic supernova, while the more recent SN 2013ek is a Type Ib. Both of these types are caused by the core collapse of massive stars that have shed — or lost — their outer layers of hydrogen. Type Ic supernovae are thought to have lost more of their outer envelope than Type Ib, including a layer of helium.

The observations that make up this new image were taken on 19 August 2013, and aimed to pinpoint the location of this new explosion more precisely. It is so close to where SN 2012im was spotted that the two events are thought to be linked; the chance of two completely independent supernovae so close together and of the same class exploding within one year of one another is a very unlikely event. It was initially suggested that SN 2013ek may in fact be SN 2012im flaring up again, but further observations support the idea that they are separate supernovae — although they may be closely related in some as-yet-unknown way.

[b][i]Credit: ESA/Hubble & NASA[/i][/b] [/quote]
[url=http://asterisk.apod.com/viewtopic.php?f=29&t=32387&p=212839#p212839][size=85][b][i]<< Previous ESA/HEIC Hubble POTW[/i][/b][/size][/url]