Free Astronomy Magazine May-June 2020

30 MAY-JUNE 2020 SPACE CHRONICLES of New Hampshire, principal investigator of the study. Lin and his team used Hubble to fol- low up on leads from NASA’s Chandra X- ray Observatory and the European Space Agency’s X-ray Multi- Mirror Mission ( XMM - N e w t o n ) , which carries three high-throughput X- ray telescopes and an optical monitor to make long uninter- rupted exposures providing highly sen- sitive observations. “Adding further X- ray observations allowed us to un- derstand the total energy output,” said team member Natalie Webb of the Université de Toulouse in France. “This helps us to understand the type of star that was disrupted by the black hole.” In 2006 these high-energy satellites detected a powerful flare of X-rays, but it was not clear if they origi- nated from inside or outside of our galaxy. Researchers attributed it to a star being torn apart after coming too close to a gravitationally power- ful compact object, like a black hole. T his is an animation of a rare and exotic intermediate-mass black hole at the centre of a star cluster, similar to the one thought to be at the centre of globular cluster Messier 15. Studying these unusual black holes could tell us about how such objects grow and evolve within both star clusters and galaxies. [NASA, ESA, and M. Kornmesser] W ide-field image around the field of J2150−0551 (ground-based view), in which an in- termediate- mass black hole named 3XMM J215022.4−055 108 has been detected. [NASA, ESA, Digitized Sky Survey 2. Ac- knowledge- ment: Davide De Martin] Deep, high-resolution imaging con- firmed that the X-rays emanated not from an isolated source in our galaxy, but instead in a distant, dense star cluster on the outskirts of another galaxy — just the sort of place astronomers expected to find evidence for an IMBH. Previous Hub- ble research has shown that the more massive the galaxy, the more massive its black hole. Therefore, this new result suggests that the star cluster that is home to 3XMM J215022.4−055108 may be the stripped-down core of a lower-mass dwarf galaxy that has been gravitationally and tidally disrupted by its close interactions with its current larger galaxy host. IMBHs have been par- ticularly difficult to find because they are smaller and less active than supermassive black holes; they do not have readily avail- able sources of fuel, nor do they have a gravitational pull that Surprisingly, the X-ray source, named 3XMM J215022.4−055108, was not located in the centre of a galaxy, where massive black holes normally reside. This raised hopes that an IMBH was the culprit, but first another possible source of the X-ray flare had to be ruled out: a neutron star in our own Milky Way galaxy, cooling off after being heated to a very high temperature. Neutron stars are the extremely dense remnants of an exploded star. Hubble was pointed at the X-ray source to resolve its precise location.