#black holes
The first picture of a black hole opens a new era of astrophysics
This is what a black hole looks like.
A world-spanning network of telescopes called the Event Horizon Telescope zoomed in on the supermassive monster in the galaxy M87 to create this first-ever picture of a black hole.
“We have seen what we thought was unseeable. We have seen and taken a picture of a black hole,” Sheperd Doeleman, EHT Director and astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., said April 10 in Washington, D.C., at one of seven concurrent news conferences. The results were also published in six papers in the Astrophysical Journal Letters.
“We’ve been studying black holes so long, sometimes it’s easy to forget that none of us have actually seen one,” France Cordova, director of the National Science Foundation, said in the Washington, D.C., news conference. Seeing one “is a Herculean task,” she said.
That’s because black holes are notoriously hard to see. Their gravity is so extreme that nothing, not even light, can escape across the boundary at a black hole’s edge, known as the event horizon. But some black holes, especially supermassive ones dwelling in galaxies’ centers, stand out by voraciously accreting bright disks of gas and other material. The EHT image reveals the shadow of M87’s black hole on its accretion disk. Appearing as a fuzzy, asymmetrical ring, it unveils for the first time a dark abyss of one of the universe’s most mysterious objects.
“It’s been such a buildup,” Doeleman said. “It was just astonishment and wonder… to know that you’ve uncovered a part of the universe that was off limits to us.”
During NASA’s Black Hole Week I saw a lot of social media posts, press releases, videos etc. that were not really correct.
One big issue with science communication about black holes is that while it has gotten good at dispelling the trivial myths (like “black holes suck everything into them and so you should be afraid Sgr A* will kill us all”) it has perpetuated other myths that require more detailed knowledge of general relativity and astronomy to debunk.
I thought it would be interesting to go over some of these misconceptions…
Another year, another Black Hole Week.
Seems like a good idea to reblog this post in case some astronomy social media managers say stuff freezes when it falls into a black hole again.
As far as the actual content of the original post, some things I would like to add:
A new misconception:
Myth: Hawking radiation comes from the event horizon of the black hole.
Reality: Hawking radiation comes from all the space-time around the black hole.
Hawking radiation is a very weak radiation all black holes are predicted to emit, and shrink down to nothing in the process. It is too weak and slow for us to detect for black holes of astrophysical size (i.e. those with the mass of stars) but if really tiny black holes exist, they could evaporate due to the radiation on timescales short enough for us to observe.
A common description of Hawking radiation in popularizations is that of matter and antimatter pairs of particles forming at the event horizon of the black hole, and one particle being sucked into the black hole and the other flying off into space as radiation. From this, one would expect the radiation to come from the event horizon, or very slightly above it.
In fact, Hawking radiation comes from a large region around the black hole, and it has the same wavelength as the size of the black hole itself. It’s like the black hole is surrounded in a diffuse bath of radiation that cannot be localized to it. This is because the particle pair description of Hawking radiation, while intuitive…is not how it actually is modeled or calculated in physics.
The actual process is too complicated for me to do calculations with (I’m a lowly astronomy & astrophysics PhD student, not a string theorist) but in general, space-time is filled with things called quantum fields. These are essentially more complex versions of stuff like the magnetic and electric fields (”classical fields”) that are more familiar. Their oscillations can appear to us as particles. When a black hole is present, it alters the possible ways the quantum fields can oscillate, like the presence of a hole in a drumskin changes the sounds the drumskin makes when you beat it. We see the new modes of oscillation as new particles.
…this is of course just an analogy, but it at least gives some idea of the physics involved.
Other notes:
-The field is leaning more and more to the idea that AGN feedback plays a major role in the quenching of star formation, at least for large spiral galaxies and the giant elliptical galaxies. That is, some form of “black holes kill galaxies” is looking more plausible as the years go by. Some form of AGN feedback appears to be necessary to get models of galaxy formation to work.
-Supermassive black holes may show jets up to higher luminosities (and so likely higher accretion rates) for their size than stellar black holes do. So the idea that quasars without visible jets lack them entirely is definitely not something that is proven at this time.
-Literally anything that has to do with what you would actually observe when you fall into a realistic astrophysical black hole that is rotating and accreting is full of disagreements between scientists. Other than that “you would die.” Remember that. “You would die.”
Why 28 + 47 = 72, Not 75, For Black Holes
“As long as space is curved and you have mass, you can’t move through it without emitting gravitational radiation. In the most severe cases of all, it even affects the way you do addition. It took 100 years from the first prediction of gravitational waves until the first direct measurement of them, and that achievement has never looked more spectacular. As our observations improve, we’ll be able to pin down more subtle effects superimposed atop this simple approximation. But for now, enjoy the simplicity of the black hole math that everyone can do!”
Want to know how much mass gets turned into energy when two black holes merge? A whopping 10% of the smaller black hole’s mass.
Must be some type of new math about two black holes merging to form a “common core.”
Hello! I’ve invented a system of space-themed xenic alignments that I’m calling the Cosmoic Alignments. I wanted to keep them completely independent of male, female, masc, and fem as well as give them a sort of abstract feel. I’ll list the alignments below, and then provide their flags in a Read More.
I want to also note that these can be used by any human or nonhuman, whether they have no gender or many genders. They also don’t have to be xenogender in order to identify with these.
Void-aligned - A formless, dark, and frigid alignment. May be unaligned or reject alignment altogether. Associated with black holes and deep space.
Constellation-aligned - A cold, multifaceted alignment that is complex and solid. May feel as though the individual parts of the alignment make up one larger alignment identity. Associated with starlight and astrology.
Nebula-aligned - A fluid, colorful, and bright alignment that floats slowly through the cold void of space. May often feel cloudy or intangible. Associated with the alignment of supernova and with stars.
Aurora-aligned - A fluctuating, colorful, and bright alignment that swirls through the temperate atmosphere. Associated with solar winds, magnetic fields, and planet Earth.
Stellar-aligned - A large, hot, and bright alignment with a fixed course through space. May be loud or boisterous. Associated with light and solar eclipses.
Supernova-aligned - A huge and red-hot alignment that seems to expand rapidly in all directions. May feel like it’s burning up other alignments around it. Associated with stars.
Planet-aligned - A stable, solid, and warm alignment thriving with liveliness. May align with both sunlight or darkness. Associated with weather patterns and gravitational forces.
Lunar-aligned - A quiet, slow, and cold alignment with a fixed course through space. May align with softness or grace. Associated with water and lunar eclipses.
Asteroid-aligned - An erratic and unpredictable alignment that is cold. May feel like it’s far away from other alignments.
Singularity-aligned - A small and enigmatic red-hot alignment that has the potential to be something bigger. May indicate questioning alignment rather than being sure.
Quantum-aligned - A paradoxical alignment that is both known and unknown, present and absent. May be complex or simple, and may overlap with many other alignments or none at all.
Language to use: “I am a cosmoic demiboy. My alignment is lunar. I am a lunar-aligned demiboy.”
** All flags are below the cut. They’re in order from top to bottom. **
nice!
production of Smol Adventures ep. 2 already in progress…
nasa:
Our Weird and Wonderful Galaxy of Black Holes
Black holes are hard to find. Like, really hard to find. They are objects with such strong gravity that light can’t escape them, so we have to rely on clues from their surroundings to find them.
When a star weighing more than 20 times the Sun runs out of fuel, it collapses into a black hole. Scientists estimate that there are tens of millions of these black holes dotted around the Milky Way, but so far we’ve only identified a few dozen. Most of those are found with a star, each circling around the other. Another name for this kind of pair is a binary system.That’s because under the right circumstances material from the star can interact with the black hole, revealing its presence.
The visualization above shows several of these binary systems found in our Milky Way and its neighboring galaxy. with their relative sizes and orbits to scale. The video even shows each system tilted the way we see it here from our vantage point on Earth. Of course, as our scientists gather more data about these black holes, our understanding of them may change.
If the star and black hole orbit close enough, the black hole can pull material off of its stellar companion! As the material swirls toward the black hole, it forms a flat ring called an accretion disk. The disk gets very hot and can flare, causing bright bursts of light.
V404 Cygni, depicted above, is a binary system where a star slightly smaller than the Sun orbits a black hole 10 times its mass in just 6.5 days. The black hole distorts the shape of the star and pulls material from its surface. In 2015, V404 Cygni came out of a 25-year slumber, erupting in X-rays that were initially detected by our Swift satellite. In fact, V404 Cygni erupts every couple of decades, perhaps driven by a build-up of material in the outer parts of the accretion disk that eventually rush in.
In other cases, the black hole’s companion is a giant star with a strong stellar wind. This is like our Sun’s solar wind, but even more powerful. As material rushes out from the companion star, some of it is captured by the black hole’s gravity, forming an accretion disk.
A famous example of a black hole powered by the wind of its companion is Cygnus X-1. In fact, it was the first object to be widely accepted as a black hole! Recent observations estimate that the black hole’s mass could be as much as 20 times that of our Sun. And its stellar companion is no slouch, either. It weighs in at about 40 times the Sun.
We know our galaxy is peppered with black holes of many sizes with an array of stellar partners, but we’ve only found a small fraction of them so far. Scientists will keep studying the skies to add to our black hole menagerie.
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