May 20, 2015

The Medusa Nebula

ESO’s Very Large Telescope in Chile has captured the most detailed image ever taken of the Medusa Nebula (also known Abell 21 and Sharpless 2-274). As the star at the heart of this nebula made its final transition into retirement, it shed its outer layers into space, forming this colourful cloud. The image foreshadows the final fate of the Sun, which will eventually also become an object of this kind.

Image Credit: ESO
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May 16, 2015

Hubble Spots the Layers of NGC 3923

NGC 3923

The glowing object in this Hubble Space Telescope image is an elliptical galaxy called NGC 3923. It is located over 90 million light-years away in the constellation of Hydra.

NGC 3923 is an example of a shell galaxy where the stars in its halo are arranged in layers.

Finding concentric shells of stars enclosing a galaxy is quite common and is observed in many elliptical galaxies. In fact, every tenth elliptical galaxy exhibits this onion-like structure, which has never been observed in spiral galaxies. The shell-like structures are thought to develop as a consequence of galactic cannibalism, when a larger galaxy ingests a smaller companion. As the two centers approach, they initially oscillate about a common center, and this oscillation ripples outwards forming the shells of stars just as ripples on a pond spread when the surface is disturbed.

NGC 3923 has over twenty shells, with only a few of the outer ones visible in this image, and its shells are much more subtle than those of other shell galaxies. The shells of this galaxy are also interestingly symmetrical, while other shell galaxies are more skewed.

Image Credit: ESA/Hubble & NASA
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May 13, 2015

Supernova SN 1987A

Supernova SN 1987A

Supernova SN 1987A, one of the brightest stellar explosions since the invention of the telescope more than 400 years ago, is no stranger to the NASA/ESA Hubble Space Telescope. The observatory has been on the frontline of studies into this brilliant dying star since its launch in 1990, three years after the supernova exploded on 23 February 1987. This image of Hubble’s old friend, retreived from the telescope’s data archive, may be the best ever of this object, and reminds us of the many mysteries still surrounding it.

Dominating this picture are two glowing loops of stellar material and a very bright ring surrounding the dying star at the centre of the frame. Although Hubble has provided important clues on the nature of these structures, their origin is still largely unknown.

Another mystery is that of the missing neutron star. The violent death of a high-mass star, such as SN 1987A, leaves behind a stellar remnant — a neutron star or a black hole. Astronomers expect to find a neutron star in the remnants of this supernova, but they have not yet been able to peer through the dense dust to confirm it is there.

The supernova belongs to the Large Magellanic Cloud, a nearby galaxy about 168 000 light-years away. Even though the stellar explosion took place around 166 000 BC, its light arrived here less than 25 years ago.

This picture is based on observations done with the High Resolution Channel of Hubble’s Advanced Camera for Surveys. The field of view is approximately 25 by 25 arcseconds.

Image Credit: ESA/Hubble & NASA
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