Since the first detection of the 1st exoplanet in 1992, astronomers have found thousands of others. Indeed, they estimate that the Milky Way is home to 40 billion worlds. So it’s easy to imagine that planet must be common in other galaxies, particularly people who seem almost like our own. But when it involves spotting these planets, there’s a prob-lem .
Other galaxies are thus far away & therefore the stars crammed into such alittle region of space, as seen from Earth, that it’s hard to spot individual ones let alone the consequences or effects of any planets around them. So extragalactic planets have sadly eluded astronomers.
Now Rosanne Di Stefano at the Harvard-Smithsonian Center for Astrophysics with several colleagues, say they found a planet in M51 Whirlpool Galaxy some 23 million light years from Earth near the constellation of Ursa Major. This alien world, christened M51-ULS-1b, is perhaps slightly smaller than Saturn & orbits binary system at a distance of perhaps 10 times Earth’s distance from Sun.
The observation was possible due to a special set of conditions. The planet’s host binary system consists of neutron’s star or black hole which is devouring an enormous nearby star at a huge rate. The infall of stardust releases huge amounts of energy, making this technique one among brightest sources of X-rays in entire Whirlpool Galaxy. Indeed, its X-ray luminosity is roughly 1,000,000 times brighter than the whole output of Sun at all wavelengths.
Hugely bright x-rays sources are rare & sparsely distributed throughout Whirlpool Galaxy.That mean they’re easy to isolate against the backdrop of ordinary stars.
And the source of those X-rays — black hole or neutron’s star is small . That mean Saturn-sized planet orbiting a billion Km away can completely eclipse the X-ray source, should it pass directly ahead in line of sight with Earth.
On Sep. 20, 2012, that’s exactly what appears to possess happened. Fortuitously, the orbiting Chandra X-ray Observatory was watching at the time. The X-ray source dimmed to zero & then reappeared, the whole transit lasting about 3 hours.
At the time, nobody noticed because the information sets from Chandra weren’t being searched for such short variations. But when Di Stefano & colleagues looked, tell tale signs were clear to see.
There are various reasons why X-ray source can dim in this way. One is that the presence of another small star, like a white dwarf star , that eclipses the X-ray source. The team says M51-ULS-1b can’t be a white dwarf star or other sort of star because binary system is just too young for such an object to possess evolved nearby.
Another potential explanation is natural variation, perhaps due to a interrupt to material falling into black hole or neutron’s star . Di Stefano & co say in these cases, the luminosity changes in characteristic way, with higher energy light frequencies changing more quickly than lower energy ones, and switching back on in different way.
But during this case, all light frequencies dimmed & reappeared at same time, suggesting an eclipse. “It is approx. symmetric, and features a shape typical of transits in which the source & transiting object have comparable size,” they say.
Now that the 1st planet candidate in another galaxy has emerged, Di Stefano & co say others are likely to be found quickly. The team scoured just some of the X-ray data from Chandra to seek out this new planet candidate.
There is plenty more where that data came from. “The archives contain enough information to conduct surveys like ours quite more than 10 times over,” say the team. “We therefore anticipate discovery of quite a dozen additional extragalactic candidate planets in wide orbits.” And more data is being gathered all the time.
So while M51-ULS-1b could also be first candidate planet discovered in another galaxy, it’s unlikely to be the last.