Ask Ethan: Can Black Holes And Dark Matter Interact?
“If you do the math, you’ll find that black holes will use both normal matter and dark matter as a food source, but that normal matter will dominate the rate of growth of the black hole, even over long, cosmic timescales. When the Universe is more than a billion times as old as it is today, black holes will still owe more than 99% of their mass to normal matter, and less than 1% to dark matter.
Dark matter is neither a good food source for black holes, nor is it (information-wise) an interesting one. What a black hole gains from eating dark matter is no different than what it gains from shining a flashlight into it. Only the mass/energy content, like you’d get from E = mc2, matters. Black holes and dark matter do interact, but their effects are so small that even ignoring dark matter entirely still gives you a great description of black holes: past, present, and future.”
You might not be able to make a black hole out of dark matter entirely, but once a black hole exists, anything that falls past its event horizon will add to its mass, whether it’s particles, antiparticles, radiation or dark matter. And the longer black holes sit in the galaxy, the more and more dark matter will eventually fall in.
The question isn’t whether dark matter contributes to black holes; it’s how and how much. Let’s give you the answer on this edition of Ask Ethan!
Astronomers Find A ‘Cloaked’ Black Hole 500 Million Years Before Any Other
“The first stars should lead to modest black holes: hundreds or thousands of solar masses. But when we see the Universe’s first black holes, they’re already ~1 billion solar masses. The leading idea is black holes form and merge, and then rapidly accrete matter at maximal rates. But those rapidly growing black holes should be invisible, obscured by the dense gas clouds they feed upon. They were, until now. New observations have revealed the earliest “cloaked” black hole ever.”
How do black holes get so big so quickly in this Universe? It’s one of the great mysteries in astrophysics, but the hope has been that better observations of the first billion years of the Universe will help solve this puzzle. If the seeds of black holes can gather enough gas around them to feed on, they just might get there. But the difficultly then comes in locating and finding these obscured, “cloaked” black holes. While they’ve been found relatively nearby, telling us that such a phenomenon does occur, they’ve never been found at very early times: within the first billion years of the Universe.
Well, with new Chandra X-ray observations, all of that has changed. We found a cloaked black hole just 850 million years after the Big Bang. It might be the key to solving this cosmic puzzle at long last.
Ask Ethan: What Has TESS Accomplished In Its First Year Of Science Operations?
“When it’s a bright, sunny day and you want to see an object in the sky that’s very close to the Sun, what do you do? You hold up a finger (or your whole hand) and block out the Sun, and then look for the nearby object that’s much intrinsically fainter than the Sun. This is exactly what telescopes equipped with coronagraphs do.
With the next generation of telescopes, this will enable us to finally directly-image planets around the closest stars to us, but only if we know where, when, and how to look. This is exactly the type of information that astronomers are gaining from TESS. By the time the James Webb Space Telescope launches in 2021, TESS will have completed its first sweep of the entire sky, providing a rich suite of tantalizing targets suitable for direct imaging. Our first picture of an Earth-like world may well be close on the horizon. Thanks to TESS, we’ll know exactly where to look.”
NASA’s TESS has completed its first year of science operations, where it’s just finished surveying the entire southern celestial hemisphere. With 13 separate observations of 27 days apiece, it’s managed to find over 800 candidate planets, including some spectacular examples of planetary systems that are unlike any we’ve ever seen before.
But the real power of TESS is that it tells us where to look to directly image Earth-sized and super-Earth-sized worlds around stars beyond our own. Find out what we’ve learned, so far, today.
Has LIGO Just Detected The ‘Trifecta’ Signal That All Astronomers Have Been Hoping For?
“Of course, all of this is just preliminary at this point. The LIGO collaboration has yet to announce a definitive detection of any type, and the IceCube event may turn out to be either a foreground, unrelated neutrino or a spurious event entirely. No electromagnetic signal has been announced, and there might not be one at all. Science moves slowly and carefully, as it should, and all of what’s been written here is a best-case scenario for the optimistic hopefuls out there, not a slam-dunk by any means.
But if we keep watching the sky in these three fundamentally different ways, and keep increasing and improving the precision at which we do so, it’s only a matter of time before the right natural event gives us the signal every astronomer has been waiting for. Just a generation ago, multi-messenger astronomy was nothing but a dream. Today, it’s not just the future of astronomy, but the present as well. There’s no moment in science quite as exciting as being on the cusp of an unprecedented breakthrough.”
There haven’t been any official releases, announcements, or claimed discoveries, but many of you may be aware that back in April, LIGO turned on again and began searching the Universe for gravitational waves, this time with improved range and sensitivity. Over that time, some 24 candidate events have been seen, and the most recent one, from July 28, 2019, is perhaps something special. Located 2.9 billion light years away and likely to be a black hole-black hole merger, it just happens to coincide with the arrival of a cosmic neutrino, in both space and time, as seen by IceCube.
Electromagnetic follow-ups are currently underway, and this could mark the first threefold multi-messenger astronomy signal ever! Watch this one closely, as it could herald a new dawn for astronomy in human history!
We Have Already Entered The Sixth And Final Era Of Our Universe
“In the end, only black dwarf stars and isolated masses to small to ignite nuclear fusion will remain, sparsely populated and disconnected from one another in this empty, ever-expanding cosmos. These final-state corpses will exist even googols of years onward, continuing to persist as dark energy remains the dominant factor in our Universe.
This last era, of dark energy domination, has already begun. Dark energy became important for the Universe’s expansion 6 billion years ago, and began dominating the Universe’s energy content around the time our Sun and Solar System were being born. The Universe may have six unique stages, but for the entirety of Earth’s history, we’ve already been in the final one. Take a good look at the Universe around us. It will never be this rich — or this easy to access — ever again.”
There are a whole slew of events and stages that the Universe has passed through over its cosmic history, and plenty of more to come as the future continues to unfold. But as far as eras of the Universe go, where things make hard transitions from one epoch to another, all of our cosmic history can be divided into six of them. From inflation to the primordial soup of the hot Big Bang to the plasma-rich early Universe to the cosmic dark ages to the stellar age to the dark energy era, our entire natural history fits nicely within these boxes.
The only existential problem? The entirety of Earth’s existence has occurred in this sixth and final era. We’re already in the end stages; see how far we’ve come and learn how far we’ll go!
Do not create a deity;
a godless sky will not forgive you
the thought-corruptive blasphemy
and blindness of staring into the endless
beginning of contradiction and measuring it
with human clock.
Deep roots of the unknown
tangle and weave stars and planets
in the spacetime fabric that
stares right back at you from the
immeasurable distance of
the first soundless explosion.
Do not create a deity:
the Thing itself knows you are there
(a miracle, you are there)
where no god would care to see you.
A part of all,
the same sacred grain-sized
pointless point shattered
and scattered in the multitude that looks back
What Makes Something A Planet, According To An Astrophysicist?
“A dolphin may look like a fish, but it’s really a mammal. Similarly, the composition of an object is not the only factor in classifying it: its evolutionary history is inextricably related to its properties. Scientists will likely continue to argue over how to best classify all of these worlds, but it’s not just astronomers and planetary scientists who have a stake in this. In the quest to make organizational sense of the Universe, we have to confront it with the full suite of our knowledge.
Although many will disagree, moons, asteroids, Kuiper belt and Oort cloud objects are fascinating objects just as worthy of study as modern-day planets are. They may even be better candidates for life than many of the true planets are. But each object’s properties are inextricably related to the entirety of its formation history. When we try to classify the full suite of what we’re finding, we must not be misled by appearances alone.”
You’ve heard about the IAU’s definition, where in order to be a planet, you must pull yourself into hydrostatic equilibrium, orbit the Sun and nothing else, and gravitationally clear your orbit. You’ve also heard about the controversial new definition from geophysical/planetary science arguments, that planets should be based on their ability to pull themselves into a spheroidal shape alone.
Well, what about a third way: defining planets (and a whole classification scheme) based on astrophysical concerns alone? It’s time to start thinking about it!
This One Species Of Animal Proves That The Moon Can Affect Biological Evolution
“The combined effects of the Moon and Sun create two tidal bulges around Earth, yielding high tides and low tides twice daily. When the Sun, Earth, and Moon all align, we get spring tides: the highest high tides possible. Tidal extremes occur during new and full Moons, with twice the magnitude of intermediate-phase neap tides. One terrestrial animal, the grunion, has uniquely adapted to take advantage of this lunar-induced phenomenon.”
There’s a species of animal out there that is absolutely reliant on the Moon for its reproductive success. The grunion, found along the pacific and baja coasts of North America, mates in an interesting fashion. The females come onto shore during high tides, where they bury the lower halves of their bodies in the sand until they stick up vertically, where they lay their eggs. The males then wrap around them, depositing sperm in an attempt to fertilize them. Now, here’s the fun thing: the eggs must remain on dry land for 10-11 days to incubate, meaning that the grunion can only do this during the highest high tides: spring tides.
Remarkably, because of our Moon’s properties and the combined tidal effects of the Moon and Sun, this enables the grunion to be an evolutionary success! Come get the full story here.
Yes, Virtual Particles Can Have Real, Observable Effects
“Now that the effect of vacuum birefringence has been observed — and by association, the physical impact of the virtual particles in the quantum vacuum — we can attempt to confirm it even further with more precise quantitative measurements. The way to do that is to measure RX J1856.5-3754 in the X-rays, and measuring the polarization of X-ray light.
While we don’t have a space telescope capable of measuring X-ray polarization right now, one of them is in the works: the ESA’s Athena mission. Unlike the ~15% polarization observed by the VLT in the wavelengths it probes, X-rays should be fully polarized, displaying right around an 100% effect. Athena is currently slated for launch in 2028, and could deliver this confirmation for not just one but many neutron stars. It’s another victory for the unintuitive, but undeniably fascinating, quantum Universe.”
If you think about empty space at a quantum level, you’ll find that it isn’t so empty, after all. Due to the inherent effects of quantum uncertainty, particle/antiparticle pairs pop into and out of existence continuously, including electrically charged particles. If you look at the quantum vacuum in the presence of a strong enough external magnetic field, the positive and negative particles, even though they’re only virtual particles, will move differently, and therefore will affect the real particles that pass through them differently than if there were no magnetic field. This leads to a real, observable signal that can be seen in space: around neutron stars!
Heisenberg first predicted this in 1936, and today, we know it’s true. Get the story of the first observable effect of vacuum birefringence today.
Sorry, Black Holes Aren’t Actually Black
“If you have an astrophysical object that emits radiation, that immediately defies the definition of black: where something is a perfect absorber while itself emitting zero radiation. If you’re emitting anything, you aren’t black, after all.
So it goes for black holes. The most perfectly black object in all the Universe isn’t truly black. Rather, it emits a combination of all the radiation from all the objects that ever fell into it (which will asymptote to, but never reach, zero) along with the ultra-low-temperature but always-present Hawking radiation.
You might have thought that black holes truly are black, but they aren’t. Along with the ideas that black holes suck everything into them and black holes will someday consume the Universe, they’re the three biggest myths about black holes. Now that you know, you’ll never get fooled again!”
So, you thought you knew all there way to know about black holes? That if you get enough mass together in a small enough volume of space, you create an event horizon: a region from within which nothing can escape, not even light. So how is it, then, that black holes wind up emitting radiation, even long after the last particle of matter to fall into them has ceased?
There are two ways this occurs, and both are completely unavoidable. Black holes aren’t actually black, and this is how we know it.