Astronomers Find Star Orbiting a Black Hole At 1 Percent the Speed of Light (sciencealert.com) 124
schwit1 writes: Astronomers have spotted a star whizzing around a vast black hole at about 2.5 times the distance between Earth and the Moon, and it takes only half an hour to complete one orbit. To put that into perspective, it takes roughly 28 days for our Moon to do a single lap around our relatively tiny planet at speeds of 3,683 km(2,288 miles) per hour. Using data from an array of deep space telescopes, a team of astronomers have measured the X-rays pouring from a binary star system called 47 Tuc X9, which sits in a cluster of stars about 14,800 light-years away. The pair of stars aren't new to astronomers -- they were identified as a binary system way back in 1989 -- but it's now finally becoming clear what's actually going on here. When a white dwarf pulls material from another star, the system is described as a cataclysmic variable star. But back in 2015, one of the objects was found to be a black hole, throwing that hypothesis into serious doubt. Data from Chandra has confirmed large amounts of oxygen in the pair's neighborhood, which is commonly associated with white dwarf stars. But instead of a white dwarf ripping apart another star, it now seems to be a black hole stripping the gases from a white dwarf. The real exciting news, however, is regular changes in the X-rays' intensity suggest this white dwarf takes just 28 minutes to complete an orbit, making it the current champion of cataclysmic dirty dancers. To put it in perspective, the distance between the two objects in X9 is about 1 million kilometers (about 600,000 miles), or about 2.5 times the distance from here to the Moon. Crunching the numbers, that's a journey of roughly 6.3 million kilometers (about 4 million miles) in half an hour, giving us a speed of 12,600,000 km/hr (8,000,000 miles/hr) - about 1 percent of the speed of light.
