Nasa cosmos images milky way
The Milky Way (left) and Andromeda (right) galaxies will collide and merge over the next several billion years NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger

A huge explosion suspected of being caused by two stars colliding in our nearest neighbouting galaxy has been described as a "false alarm" by Nasa.

Enthusiastic followers of astronomy thought Nasa's Swift satellite detected a burst of high-energy gamma rays coming from the Andromeda galaxy. The explosion was so powerful that if it happened in our galaxy, life on Earth would end.

But after much hype on social media, the Swift BAT (Burst Alert Telescope) team confirmed the unusual sighting was just a neutron star orbiting a normal star, which was shining brighter than normal due to faulty data analysis.

"Why it has been reported throughout the web as a GRB (gamma-ray burst) is something I can only speculate on, but Swift has been fabulously successful studying GRBs. Indeed it was ranked #1 by Nasa this month. I guess that enthusiastic followers of astronomy put two and two together and made five, unfortunately," wrote Phil Evans on star.le.ac.uk.

"I've even read people saying that there were loads of gamma rays from this object: there definitely weren't. In fact, the Swift-Bat Team said that 'this is a faint BAT transient'."

Kim Page at University of Leicester sent out this circular today to dismiss rumours there had been a gamma-ray Burst.

Nasa's Swift Burst Alert Telescope watches the skies for gamma-ray bursts and observes around 90 events a year, but usually from further afield.

The initial alert prompted much excitement on Twitter, including from comedian Dara O'Briain.