Evidence of Planet in Another Galaxy

The astronomers have found the first-ever evidence of a planet in another galaxy. The astronomers detected thousands of worlds since exoplanet 1992. According to astronomers, Milky Way is full of planets. Now astronomers have found the first candidate planet in another galaxy.

There is an estimation of 40 billion worlds in the Milky Way by the astronomers. There is a supposition of a similar estimate of planets in other galaxies as well, especially for the ones that are similar to ours.

Spotting Problem

The spotting of the planets is not easy and got problems. Other galaxies are so far away and the stars crammed into such a small region of space, as seen from Earth, that it is hard to identify individual ones, let alone the effects of any planets around them. So extragalactic planets have sadly eluded astronomers.

Harvard-Smithsonian Center for Astrophysics

Rosanne Di Stefano at the Harvard-Smithsonian Center for Astrophysics and several colleagues say they have found a candidate planet in the M51 Whirlpool Galaxy some 23 million light-years from Earth near the constellation of Ursa Major. This alien world, christened M51-ULS-1b, is probably slightly smaller than Saturn and orbits a binary system at a distance of perhaps ten times Earth’s distance from the Sun.

Research Conditions

The observation was possible because of a particular set of conditions. The planet’s host binary system consists of a neutron star or black hole devouring a massive nearby star at a tremendous rate. The infall of stardust releases enormous amounts of energy, making this system one of the brightest sources of X-rays in the entire Whirlpool Galaxy. Indeed, its X-ray luminosity is roughly a million times brighter than the whole output of the Sun at all wavelengths.

Hugely bright x-rays sources are rare and sparsely distributed throughout the Whirlpool Galaxy. That means they are easy to isolate against the backdrop of ordinary stars.

X-Rays Source

The source of the X-rays — the black hole or neutron star — is tiny. This means that a Saturn-sized planet orbiting a billion kilometers away can completely eclipse the X-ray source, should it pass directly in front in the line of sight with Earth.

On Sep. 20, 2012, that was precisely what appears to have happened. Fortuitously, the orbiting Chandra X-ray Observatory was watching at the time. The X-ray source dimmed to nothing and then reappeared, the entire transit lasting about 3 hours.

At the time, nobody noticed because the data sets from Chandra weren’t being searched for such short variations. But when Di Stefano and colleagues looked, the telltale signs were clear to see.

There are various reasons why an X-ray source can dim in this way. One is the presence of another small star, such as a white dwarf, that eclipses the X-ray source. The team says M51-ULS-1b cannot be a white dwarf or another type of star because the binary system is too young for such an object to have evolved nearby.

Another potential explanation is natural variation, perhaps because of an interruption to the material falling into the black hole or neutron star. Di Stefano and co say in these cases, the luminosity changes in a characteristic way, with higher energy light frequencies changing more quickly than lower-energy ones and switching back on in a different way.

Transit Time

In this observation, all the light frequencies dimmed and reappeared at the same time, suggesting an eclipse. “It is approximately symmetric, and has a shape typical of transits in which the source and transiting object have comparable size”.

Now that the first planet candidate in another galaxy has emerged, Di Stefano and co say others are likely to be found quickly. The team scoured just a portion of the X-ray data from Chandra to see this new planet candidate.

There is plenty more where that data came from. “The archives contain enough data to conduct surveys comparable to ours more than ten times over,” said the team. “We, therefore, anticipate the discovery of more than a dozen additional extragalactic candidate planets in wide orbits.” And more data is being gathered all the time.

So while M51-ULS-1b may be the first candidate planet discovered in another galaxy, it is unlikely to be the last. Just watch this space.