The jet emerging from the galactic core of M87. NASA/STScI/AURA.
Everyone loves a good mystery, and astronomers have just uncovered a new one in a nearby supermassive galaxy called M87. Like most galaxies, M87 regularly plays host to a smattering of stellar explosions called novae, each the result of a star stealing material from a neighbour. M87 also features a massive jet of plasma blasting out into deep space from the galactic core. These phenomena: the jet and the novae, are unrelated astronomical occurrences, or so scientists believed. But astronomers recently discovered that the novae in M87 seem to be uncharacteristically aligned along the jet, instead of scattered randomly throughout the galaxy. Is the jet somehow triggering nova explosions?
Patterns in nature often occur in more than one place. Spirals, symmetry, and chaos all impact natural phenomena, from the shape of a shell to the course of a river. So it shouldn’t come as a surprise that one of the most famous and fundamental shapes from biology also appears in astrophysics. Yes, scientists have found a double-helix structure in the magnetic field of M87. And it looks just like a super enlarged DNA strand.
Credit: M. Janssen, H. Falcke, M. Kadler, E. Ros, M. Wielgus et al.
On April 10th, 2019, the world was treated to the first image of a black hole, courtesy of the Event Horizon Telescope (EHT). Specifically, the image was of the Supermassive Black Hole (SMBH) at the center of the supergiant elliptical galaxy known as M87 (aka. Virgo A). These powerful forces of nature are found at the centers of most massive galaxies, which include the Milky Way (where the SMBH known as Sagittarius A* is located).
Using a technique known as Very-Long-Baseline Interferometry (VLBI), this image signaled the birth of a new era for astronomers, where they can finally conduct detailed studies of these powerful forces of nature. Thanks to research performed by the EHT Collaboration team during a six-hour observation period in 2017, astronomers are now being treated to images of the core region of Centaurus A and the radio jet emanating from it.
Computer Simulation of a Quasar, a Supermassive Black Hole that is actively feeding and creating tremendous energy - created in "SpaceEngine" pro by author
A monster lurks at the heart of many galaxies – even our own Milky Way. This monster possesses the mass of millions or billions of Suns. Immense gravity shrouds it within a dark cocoon of space and time – a supermassive black hole. But while hidden in darkness and difficult to observe, black holes can also shine brighter than an entire galaxy. When feeding, these sleeping monsters awaken transforming into a quasar – one of the Universe’s most luminous objects. The energy a quasar radiates into space is so powerful, it can interfere with star formation for thousands of light years across their host galaxies. But one galaxy appears to be winning a struggle against its awoken blazing monster and in a recent paper published in the Astrophysical Journal, astronomers are trying to determine how this galaxy survives.
Using NASA’s Chandra X-ray Observatory, astronomers have seen that the famous giant black hole in Messier 87 is propelling particles at speeds greater than 99% of the speed of light. Image Credit: NASA/CXC/SAO/B. Snios et al.
Can black holes be famous? If they can, then the one at the heart of the M87 galaxy qualifies. And this famous black hole is emitting jets of material that travel at near the speed of light.
A Hubble Space Telescope view of M87's core and its jet. it points nearly directly at us and is also known as a blazar. Astronomers are studying other blazars that have meandering jets and think that binary black holes may be hidden inside some of them. Courtesy STScI.
Black holes are the one the most intriguing and awe-inspiring forces of nature. They are also one of the most mysterious because of the way the rules of conventional physics break down in their presence. Despite decades of research and observations there is still much we don’t know about them. In fact, until recently, astronomers had never seen an image of black hole and were unable to guage their mass.
However, a team of physicist from the Moscow Institute of Physics and Technology (MIPT) recently announced that they had devised a way to indirectly measure the mass of a black hole while also confirming its existence. In a recent study, they showed how they tested this method on the recently-imaged supermassive black hole at the center of the Messier 87 active galaxy.
The Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes forged through international collaboration — was designed to capture images of a black hole. In coordinated press conferences across the globe, EHT researchers revealed that they succeeded, unveiling the first direct visual evidence of the supermassive black hole in the centre of Messier 87 and its shadow. The shadow of a black hole seen here is the closest we can come to an image of the black hole itself, a completely dark object from which light cannot escape. The black hole’s boundary — the event horizon from which the EHT takes its name — is around 2.5 times smaller than the shadow it casts and measures just under 40 billion km across. While this may sound large, this ring is only about 40 microarcseconds across — equivalent to measuring the length of a credit card on the surface of the Moon. Although the telescopes making up the EHT are not physically connected, they are able to synchronize their recorded data with atomic clocks — hydrogen masers — which precisely time their observations. These observations were collected at a wavelength of 1.3 mm during a 2017 global campaign. Each telescope of the EHT produced enormous amounts of data – roughly 350 terabytes per day – which was stored on high-performance helium-filled hard drives. These data were flown to highly specialised supercomputers — known as correlators — at the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory to be combined. They were then painstakingly converted into an image using novel computational tools developed by the collaboration. Credit: Event Horizon Telescope Collaboration
“We have taken the first picture of a black hole.”
EHT project director Sheperd S. Doeleman of the Center for Astrophysics | Harvard & Smithsonian.
What was once un-seeable can now be seen. Black holes, those difficult-to-understand singularities that may reside at the center of every galaxy, are becoming seeable. The Event Horizon Telescope (EHT) has revealed the first-ever image of a black hole, and with this image, and all the science behind it, they may help crack open one of the biggest mysteries in the Universe.
We talk about stellar mass and supermassive black holes. What are the limits? How massive can these things get?
Without the light pressure from nuclear fusion to hold back the mass of the star, the outer layers compress inward in an instant. The star dies, exploding violently as a supernova.
All that’s left behind is a black hole. They start around three times the mass of the Sun, and go up from there. The more a black hole feeds, the bigger it gets.
Terrifyingly, there’s no limit to much material a black hole can consume, if it’s given enough time. The most massive are ones found at the hearts of galaxies. These are the supermassive black holes, such as the 4.1 million mass nugget at the center of the Milky Way. Astronomers figured its mass by watching the movements of stars zipping around the center of the Milky Way, like comets going around the Sun.
There seems to be supermassive black holes at the heart of every galaxy we can find, and our Milky Way’s black hole is actually puny in comparison. Interstellar depicted a black hole with 100 million times the mass of the Sun. And we’re just getting started.
The giant elliptical galaxy M87 has a black hole with 6.2 billion times the mass of the Sun. How can astronomers possibly know that? They’ve spotted a jet of material 4,300 light-years long, blasting out of the center of M87 at relativistic speeds, and only black holes that massive generate jets like that.
Most recently, astronomers announced in the Journal Nature that they have found a black hole with about 12 billion times the mass of the Sun. The accretion disk here generates 429 trillion times more light than the Sun, and it shines clear across the Universe. We see the light from this region from when the Universe was only 6% into its current age.
Somehow this black hole went from zero to 12 billion times the mass of the Sun in about 875 million years. Which poses a tiny concern. Such as how in the dickens is it possible that a black hole could build up so much mass so quickly? Also, we’re seeing it 13 billion years ago. How big is it now? Currently, astronomers have no idea. I’m sure it’s fine. It’s fine right?
We’ve talked about how massive black holes can get, but what about the opposite question? How teeny tiny can a black hole be?
An illustration that shows the powerful winds driven by a supermassive black hole at the centre of a galaxy. The schematic figure in the inset depicts the innermost regions of the galaxy where a black hole accretes, that is, consumes, at a very high rate the surrounding matter (light grey) in the form of a disc (darker grey). At the same time, part of that matter is cast away through powerful winds. (Credits: XMM-Newton and NuSTAR Missions; NASA/JPL-Caltech;Insert:ESA)
Astronomers figure there could be primordial black holes, black holes with the mass of a planet, or maybe an asteroid, or maybe a car… or maybe even less. There’s no method that could form them today, but it’s possible that uneven levels of density in the early Universe might have compressed matter into black holes.
Those black holes might still be out there, zipping around the Universe, occasionally running into stars, planets, and spacecraft and interstellar picnics. I’m sure it’s the stellar equivalent of smashing your shin on the edge of the coffee table.
Astronomers have never seen any evidence that they actually exist, so we’ll shrug this off and choose to pretend we shouldn’t be worrying too much. And so it turns out, black holes can get really, really, really massive. 12 billion times the mass of the Sun massive.
What part about black holes still make you confused? Suggest some topics for future episodes of the Guide to Space in the comments below.
This artist's illustration shows the hypervelocity star cluster HVGC-1 escaping from the supergiant elliptical galaxy M87. HVGC-1 is the first runaway star cluster discovered by astronomers. It is fated to drift through intergalactic space.
David A. Aguilar (CfA)
We’ve discovered dozens of so-called “hypervelocity stars” — single stars that break the stellar speed limit. But today astronomers multiplied the number of these ‘runaway’ stars by hundreds of thousands. The Virgo Cluster galaxy, M87, has ejected an entire star cluster, throwing it toward us at more than two million miles per hour.
“Astronomers have found runaway stars before, but this is the first time we’ve found a runaway star cluster,” said lead author Nelson Caldwell of the Harvard-Smithsonian Center for Astrophysics, in a press release.
About one in a billion stars travel at a speed roughly three times greater than our Sun (which clocks in at 220 km/s with respect to the galactic center). At a speed that fast, these stars can easily escape the galaxy entirely, traveling rapidly throughout intergalactic space.
But this is the first time an entire star cluster has broken free.
What would cause an entire cluster — hundreds of thousands of stars packed together a million times more closely than in the neighborhood of our Sun — to reach such a tremendous speed?
Single hypervelocity stars have puzzled astronomers for years. But by observing their speed and direction, astronomers can trace these stars backward, finding that some began moving quickly in the Galactic Center. Here, an interaction with the supermassive black hole can kick a star away at an alarming speed. Another option is that a supernova explosion propelled a nearby star to a huge speed.
Caldwell and colleagues think M87 might have two supermassive black holes at its center. The star cluster wandered too close to the pair, which picked off many of the cluster’s outer stars while the inner core remained intact. The black holes then acted like a slingshot, flinging the cluster away at a tremendous speed.
The star cluster is moving so fast it should soon by sailing into intergalactic space. It may already be, but its distance remains unknown.
Velocities of stars, globular clusters and galaxies toward Virgo. HVGC-1 is the marked extreme left outlier. Image Credit: Caldwell et al.
The team found the globular cluster — dubbed HVGC-1 — with a stroke of luck. They had been analyzing 2,500 globular cluster candidates for years. While a computer algorithm automatically calculated the speed of every cluster, any oddity was analyzed by hand.
Over 1,000 candidates have measured velocities between 500 and 3000 km/s. These speeds are typical for Virgo Cluster members. But HVGC-1 has a radial velocity of -1026 km/s. “This is the most negative, bulk velocity ever measured for an astronomical object not orbiting another object,” writes Caldwell.
“We didn’t expect to find anything moving that fast,” said coauthor Jay Strader of Michigan State University.
Future measurements pinpointing the exact distance to the globular cluster will help shed light on its exact origins.
The paper will be published in The Astrophysics Journal Letters and is available for download here.
