Updated:04/06/2020 01: 24h
They have been elusive with human science since it was postulated that they existed. But now a “crime” in the cosmos has betrayed its existence: an intermediate-mass black hole has revealed its position by ripping apart a stray star that passed too close.
Weighing about 50,000 times the mass of our Sun, it is straddling the gigantic supermassive black holes (millions or billions of solar masses) found in the nuclei of large galaxies and the smaller black holes that they form after the colpaso of a massive star. These so-called intermediate-mass black holes (IMBHs) are the long-sought “missing link” in the evolution of black holes. Although there have been a few other candidates for IMBH, the researchers consider these new observations to be the strongest evidence to date for finding that medium-sized black holes exist in the universe.
And to account for them, it took the combined power of two X-ray observatories and NASA’s Hubble Space Telescope to catch this cosmic beast. “Intermediate mass black holes are very difficult to reach objects, so it is essential to carefully consider and discard alternative explanations for each candidate. That is what Hubble has allowed us to do, “he says. Dacheng Lin, from the University of New Hampshire, principal investigator of the study. The results have been published this week ‘The Astrophysical Journal Letters’.
In search of the missing link
Lin and his team used Hubble to track tracks from NASA’s Chandra X-ray observatory and the European Space Agency’s (ESA) XMM-Newton. In 2006, these satellites detected a powerful x-ray flareBut they couldn’t determine if it originated inside or outside our galaxy. The researchers attributed it to a star that tore apart after getting too close to a gravitationally powerful compact object, such as a black hole.
Surprisingly, the X-ray source, called 3XMM J215022.4-055108, was not located in the center of a galaxy, where massive black holes would normally reside. This raised hopes that an intermediate-mass black hole was to blame, but another possible source of the X-ray flare had to be ruled out first: a neutron star in our own galaxy, the Milky Way, which cools down after warming up. at a very high temperature -the neutron stars they are the crushed remains of an exploded star.
A drifting galaxy core
Hubble aimed at the X-ray source to figure out its precise location. Deep high-resolution images provide strong evidence that X-rays did not emanate from an isolated source in our galaxy, but from a distant, dense star cluster just outside another cosmic neighborhood, just the kind of place astronomers expected. find IMBH. Previous Hubble research has shown that the mass of a black hole at the center of a galaxy is proportional to the central protuberance of that host galaxy. In other words, the more massive the galaxy is, the more massive its black hole is. Therefore, the star cluster that houses the 3XMM J215022.4-055108 may be the stripped core of a lower-mass dwarf galaxy that has been gravitationally and tidally disrupted by its close interactions with its current largest galaxy host.
IMBHs have been particularly difficult to find because they are smaller and less active than supermassive black holes; They do not have readily available fuel sources, nor such a strong gravitational pull to attract stars and other cosmic materials that would produce telltale X-ray flares. Astronomers essentially have to catch an IMBH red-handed while gobbling up a star. Lin and colleagues reviewed the XMM-Newton data file, searching hundreds of thousands of observations to find an IMBH candidate.
The X-ray glare from the crushed star allowed astronomers to estimate the black hole’s mass of 50,000 solar masses. The IMBH mass was estimated based on the X-ray luminosity and the spectral shape. “This is much more reliable than using only X-ray brightness, as was done before for pre-IMBH candidates,” says Lin. it’s a statement. “The reason we can use spectral adjustments to estimate the IMBH mass for our object is that its spectral evolution showed that it has been in the thermal spectral state, a state commonly seen and well understood in the accumulation of stellar-mass black holes ».
Not the first candidate
This object is not the first to be considered a likely candidate for an intermediate-mass black hole. In 2009, Hubble partnered with NASA’s Swift Observatory and ESA’s XMM-Newton to identify what is interpreted as an IMBH, called HLX-1, located toward the edge of the ESO 243-49 galaxy. It is also at the center of a young and massive group of blue stars that may be a stripped dwarf galaxy core. X-rays come from a hot accretion disk around the black hole.
“The main difference is that our object is to tear apart a star, which provides strong evidence that it is a massive black hole, rather than a stellar-mass black hole, as people often care about previous candidates, including HLX-1, ”explains Lin.
Finding this IMBH opens the door to the possibility that many more are lurking undetected in the dark, waiting to be gifted by a star that passes too close. Lin plans to continue her meticulous detective work, using methods that her team has proven successful. Many questions remain to be answered: Does a supermassive black hole grow from an IMBH? How are the IMBHs themselves formed? Are the dense star clusters your favorite home?