A giant interstellar bubble being grown in the Andromeda Galaxy

Composite image - A giant interstellar bubble being grown in the Andromeda Galaxy
This is a composite image of Liverpool Telescope data (bottom left) and Hubble Space Telescope data (top right) of the nova super-remnant. M31N 2008-12a is in the middle of the image.

An international team of astrophysicists have uncovered an enormous bubble current being ‘blown’ by the regular eruptions from a binary star system within the Andromeda Galaxy.

Recent observations with the Liverpool Telescope and Hubble Space Telescope, supported by spectroscopy from the Gran Telescopio Canarias, and the Hobby Eberly Telescope (some of the largest astronomy facilities on Earth) discovered this enormous shell-like nebula surrounding ‘M31N 2008-12a’, a recurrent novae located in our neighbouring Andromeda Galaxy.

At almost 400 lightyears across – and still growing, this shell is far bigger a typical nova remnant (usually around a lightyear in size) and even larger than most supernova remnants. 

Dr Matt Darnley, lead author on the study and Reader in Time Domain Astrophysics at LJMU’s Astrophysics Research Institute explains:

“Each year ‘12a’ (as we lovingly refer to it) undergoes a thermonuclear eruption on the surface of its white dwarf. These are essentially hydrogen bombs, which eject material equivalent to about the mass of the Moon in all directions at a few 1000 kilometres per second. These ejecta act like a snow plough, piling the surrounding ‘interstellar medium’ up to form the shell we observe – the outer ‘skin’ of the bubble, or the ‘super-remnant’ as we have named it.”

These new observations coupled with state-of-the-art hydrodynamic simulations (carried out at LJMU and the University of Manchester) have revealed that this vast shell is in fact the remains of not just one nova eruption but possibly millions – all from the same system. 

Despite its uniqueness and staggering scale, the discovery of this super-remnant may have further significance.

Dr Matt Darnley continued: “Studying 12a and its super-remnant could help to understand how some white dwarfs grow to their critical upper mass and how they actually explode once they get there as a ‘Type Ia Supernova’. Type Ia supernovae are critical tools used to work out how the universe expands and grows.” 

In a related work, also led by Matt Darnley, this team has predicted that 12a will ultimately explode as a Type Ia Supernova in less than 20,000 years – a very short time in cosmological terms.

Dr Rebekah Hounsell, second author on both studies and a post-doctoral researcher at the University of Pennsylvania, was at the Space Telescope Science Institute when she took part in the research. She explains:

“Type Ia supernovae are some of the largest explosions in the Universe and our most mature cosmological probes. The recurrent novae M31N 2008-12a is the most likely SN Ia progenitor to date, and provides us with the unique opportunity to study such a system before its final demise.

“Lying within our nearest galactic neighbour, Andromeda, the explosion of 12a would be one of the closest supernovae observed by telescopes. The last observed supernova within our own galaxy occurred in 1604. Although we predict that 12a will undergo its explosion in less than twenty thousand years, there is the possibility of it happening within the next decade or so.”

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