The APOD { http://apod.nasa.gov/apod/ap151119.html } for 2015 November 19 shows
ID: 1836448 • Letter: T
Question
The APOD { http://apod.nasa.gov/apod/ap151119.html } for 2015 November 19 shows a detailed image of the nearby "peculiar elliptical" galaxy Centaurus A. This galaxy doesn't look like an elliptical to me! I thought elliptical galaxies are "red and dead". The explanation says that this galaxy is "forged in a collision of two otherwise normal galaxies", and contains "young blue star clusters" and "star-forming regions". Can you describe a simple scenario in which a collision might end up producing a galaxy that looks like this one?
Explanation / Answer
The center of the galaxy contains a supermassive black hole with a mass equivalent to 55 million solar masses, which ejects a relativistic jet that is responsible for emissions in the X-ray and radio wavelengths. Models have suggested that Centaurus A was a large elliptical galaxy which collided and merged with a smaller spiral galaxy. The galaxy's strange morphology is generally recognized as the result of a merger between two smaller galaxies.
Two Supernovae have been detected in Centaurus A. The first supernova, named SN 1986G, was discovered within the dark dust lane of the galaxy by R. Evans in 1986. It was later identified as a type Ia supernova, which forms when a white dwarf's mass grows large enough to ignite carbon fusion in its center, touching off a runaway thermonuclear reaction, as may happen when a white dwarf in a binary star system strips gas away from the other star. SN 1986G was used to demonstrate that the spectra of type Ia supernovae are not all identical, and that type Ia supernovae may differ in the way that they change in brightness over time. Presence of young bright stars which can be responsible for colour of the galaxy.
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