Since the first extrasolar planet was discovered in 1992, astronomers have discovered thousands of other extrasolar planets. In fact, they estimate that our galaxy has about 40 billion planets. So it’s natural to think that there will be many planets in other galaxies, especially those that look a little bit like our own. But there’s a problem with finding these planets. < / P > < p > from our earth, other galaxies are so far away, and stars seem to be crowded in a very small area. This makes it difficult to identify individual galaxies, let alone any influence of the surrounding planets. So, extragalactic planets have so successfully escaped the search of astronomers. < / P > < p > recently, however, rozan Di Stefano of the Harvard Smithsonian Center for Astrophysics and several colleagues said they had found a candidate planet in the M51 spiral galaxy. M51 is located near the constellation Ursa Major, about 23 million light-years away from earth. Named “m51-uls-1b”, this alien world may be a little smaller than Saturn, orbiting a binary system about ten times the distance between the earth and the sun. < / P > < p > because of a series of special conditions, observation is possible. The planet’s binary system contains a neutron star or black hole, which engulfs nearby stars at great speed. The dust inhalation will release a lot of energy, making the binary system the brightest source of X-ray in the whole vortex galaxy. In fact, the X-ray brightness of the binary system is a million times brighter than the total brightness of all wavelengths of sunlight. < / P > < p > but the source of these X-rays, black holes or neutron stars, is very small. This means that the planet, the size of Saturn, orbiting a billion kilometers away, can completely block the X-ray source if it moves in line with the earth and is directly in front of the X-ray source. < / P > < p > this special phenomenon happened on September 20, 2012. Fortunately, the Chandra X-ray Observatory also observed this phenomenon at that time. The X-ray source gradually disappeared to zero, and then gradually recovered. The whole transit process lasted about 3 hours. < / P > < p > no one noticed this phenomenon at that time, because no one had searched the Chandra observatory data set for such a short change. But then, when di stafano and his colleagues saw the data, they immediately saw the clue. < / P > < p > X-ray sources darken in this way for many reasons. One is the presence of another small star, such as a white dwarf, blocking the X-ray source. However, the team does not think that uls-m51b or uls-1b could be a white dwarf for long enough. < / P > < p > another possible explanation is natural change, that is, the sudden interruption of matter falling into a black hole or neutron star. Di stafano and his colleagues said that if so, the brightness change will have certain characteristics, the frequency change of high-energy light will be faster than that of low-energy light, and the recovery method will be different. < / P > < p > but in this phenomenon observed by Chandra X-ray Observatory, all the light frequencies disappear and recover at the same time, which is more like an erosion phenomenon. “It’s nearly symmetrical and has a typical shape of a transit star, where the light source is the same size as the transit star,” they said. < / P > < p > now that the first planet candidates for other galaxies have appeared, di stafano and colleagues believe that other extragalactic planets should also be found soon. The team searched only part of the X-ray data from the Chandra X-ray Observatory and found the new planet candidate. There are many sources of < / P > < p > data. “These archives contain enough data for us to do more research,” the team said, “so we expect to find more than a dozen candidates for extragalactic planets in the future.” At the same time, new data are accumulating. < / P > < p > so m51-uls-1b may be the first planet candidate we find in other galaxies, but it won’t be the last. (Qi Lin) < a= target=_ blank>Privacy Policy