The galaxy NGC 691 in the constellation Aries presents a stunning target for the Hubble Space Telescope, showing off near perfect spiral arms wrapped tightly around a brilliant core. Discovered by William Herschel in November 1786, NGC 691 is about 120 million light years from the Milky Way and measures some 130,000 light years across. A type 1a supernova, a class used as “standard candles” in surveys supporting the discovery of dark energy, was detected in NGC 691 in 2005.
A new study finds that elliptical galaxies maintain a remarkably constant circular speed out to large distances from their centres, in the same way that spiral galaxies do. In these very different types of galaxies, stars and dark matter somehow conspire to redistribute themselves to produce this effect, or does modified Newtonian dynamics offer an explanation?
In this season of post-Christmas gym memberships, black holes have shown that they too can lose a lot of the weight of the stars that surround them. One unusually star-deprived black hole at the site of two merged galaxies could provide new insight into black hole evolution and behaviour, according to observations with the Hubble Space Telescope and Chandra X-ray Observatory.