Black holes are long-time superstars of science fiction. But their Hollywood fame is a little strange given that no-one has ever actually seen one – at least, until now. If you needed to see to believe, then thank the Event Horizon Telescope (EHT), which has just produced the first ever direct image of a black hole. This amazing feat required global collaboration to turn the Earth into one giant telescope and image an object thousands of trillions of kilometres away.
Late in 2018, the gravitational wave observatory, LIGO, announced that they had detected the most distant and massive source of ripples of spacetime ever monitored: waves triggered by pairs of black holes colliding in deep space. Only since 2015 have we been able to observe these invisible astronomical bodies, which can be detected only by their gravitational attraction. The history of our hunt for these enigmatic objects traces back to the 18th century, but the crucial phase took place in a suitably dark period of human history – World War II.
Four new detections of gravitational waves have been announced at the Gravitational Waves Physics and Astronomy Workshop, at the University of Maryland in the United States.
A fountain in a garden pond could shoot a plume of water to roughly three metres in height. By comparison, the famous fountain on Lake Geneva launches a plume of water up to 140m into the air. Now imagine a fountain launched from the centre of a galaxy, with a supermassive black hole acting as the pump. How far do you think this plume would extend? The answer is over 100,000 light years.
Observations made with ESO’s Very Large Telescope have for the first time revealed the effects predicted by Einstein’s general relativity on the motion of a star passing through the extreme gravitational field near the supermassive black hole in the centre of the Milky Way. This long-sought result represents the climax of a 26-year-long observation campaign using ESO’s telescopes in Chile.
About a decade ago, astronomers discovered a population of small, but massive galaxies called “red nuggets.” A new study using NASA’s Chandra X-ray Observatory indicates that black holes have squelched star formation in these galaxies and may have used some of the untapped stellar fuel to grow to unusually massive proportions.
Astronomers first noticed an enigmatic object, dubbed “Sagittarius A*”, at the very heart of our Milky Way galaxy in the 1960s – the earliest days of radio and infrared astronomy. But just how extraordinary this source was only became clear three decades later, when it was identified as a supermassive black hole with the mass of whopping four million suns.
During the 1960s, scientists discovered a massive radio source (known as Sagittarius A*) at the center of the Milky Way, which was later revealed to be a Supermassive Black Holes (SMBH). Since then, they have learned that these SMBHs reside at the center of most massive galaxies. The presence of these black holes is also what allows the centers of these galaxies to have a higher than normal luminosity – aka. Active Galactic Nuclei (AGNs).
Astronomers have been fascinated with globular clusters ever since they were first observed in 17th century. These spherical collections of stars are among the oldest known stellar systems in the Universe, dating back to the early Universe when galaxies were just beginning to grow and evolve. Such clusters orbit the centers of most galaxies, with over 150 known to belong to the Milky Way alone.
In the 1970s, astronomers discovered that a particularly large black hole (Sagittarius A*) existed at the center of our galaxy. In time, they came to understand that similar Supermassive Black Holes (SMBHs) existed in the center of most massive galaxies. The presence of these black holes was also what differentiated galaxies that had particularly luminous cores – aka. Active Galactic Nuclei (AGN) – from those that didn’t.
Encountering a black hole would be a frightening prospect for our planet. We know that these cosmic monsters ferociously devour any object that strays too close to their “event horizon” – the last chance of escape. But even though black holes drive some of the most energetic phenomena in the universe, the physics of their behaviour, including how they feed, remains hotly debated.
Monster black holes sometimes lurk behind gas and dust, hiding from the gaze of most telescopes. But they give themselves away when material they feed on emits high-energy X-rays that NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) mission can detect. That's how NuSTAR recently identified two gas-enshrouded supermassive black holes, located at the centers of nearby galaxies.
Ever since the discovery of Sagittarius A* at the center of our galaxy, astronomers have come to understand that most massive galaxies have a Supermassive Black Hole (SMBH) at their core. These are evidenced by the powerful electromagnetic emissions produced at the nuclei of these galaxies – which are known as “Active Galatic Nuclei” (AGN) – that are believed to be caused by gas and dust accreting onto the SMBH.
For decades, astronomers have known that Supermassive Black Holes (SMBHs) reside at the center of most massive galaxies. These black holes, which range from being hundreds of thousands to billions of Solar masses, exert a powerful influence on surrounding matter and are believed to be the cause of Active Galactic Nuclei (AGN). For as long as astronomers have known about them, they have sought to understand how SMBHs form and evolve.