What Is a Blazar? It’s Like Staring Down the Barrel of a Black Hole | Hacker News Reader

What Is a Blazar? It’s Like Staring Down the Barrel of a Black Hole

blogs.discovermagazine.com

69 pointseaguyhn29 comments

I'm always astounded by the pictures that are associated with black holes. Absolutely none of them are representative of what we've actually seen...because we've never directly imaged a black hole.

I'm not even sure if we can image it, because theoretically, we're imaging the stuff around them aka the event horizon or other matter which is being acted on by the black hole.

I mention this because it's one of the best examples Along with the electron) where we have such a strong desire to create visual representation of something we can't actually perceive because our minds require visual representation to understand the concept.

We should have our first picture soon: https://eventhorizontelescope.org/blog/eht-status-update-may...

Don't tease me with their May update again :(

Well, slight semantic nuances of English aside, we absolutely have taken pictures of black-hole-emitted radiation; see [0] for an example. Search for photos of X-ray emissions. It's true that most of the energy seen from the direction of a black hole will be leftover scraps from its messy eating habits, but Hawking radiation should be a thing (although we'll likely never observe it above the CMBR), and rotating black holes should also be a thing.

If you decide to go the fuzzball route, then perception without direct visualization isn't too hard, aside from the holographic principle, which helpfully justifies the idea that fuzzballs are a place where 3D movement becomes 2D movement. On a fuzzball, you might imagine strings moving around on the surface, but there's no meaningful way to move further into the fuzzball nor to detach from the surface and leave, aside from getting lots of energy and popping off as Hawking radiation/firewall. Incidentally, 2D movement is something that we have tons of intuition for already!

[0] https://www.space.com/35231-deepest-x-ray-image-black-holes....

Edit: Many folks would consider our gravitational-wave telescopes, like LIGO, to give us data which could be interpreted visually. [1]

[1] https://www.youtube.com/watch?v=I_88S8DWbcU

This is exactly my point and the semantics do matter here because they relate to the epistemic nature of the content. Namely that humans can't directly interpret X-Rays (or other non-visible light emissions).

We have to convert X-Ray emissions into images or mathematical representations which we then interpret visually/logically. So there is some level of information compression which we have to do just to be able to do some interpretation.

This is not a hit on them at all, in fact it's a genius workaround. All I really want to point out here really is the limits to our perception and the lengths that we go to, in order to transform non-perceivable phenomena into into modalities that we can perceive. It's an exercise in investigating the boundaries of our epistemic capabilities.

Strictly speaking we don't see colours at all, we just hallucinate them from the monochrome response in three (or fewer) filters. So, for example, we commonly confuse mixes of different colours with a colour between them.

In this strict frame of mind, it is not a trivial epistemic statement to say that "the highlight colour at yellow.com is yellow", since your screen can not physically emit yellow light.

Yes, the rabbit hole goes deep in the perception question. Which is why I think it's important that we recognize the nested abstractions when we are trying to describe concepts - especially when they are interpreted from things that we don't have even fundamental perceptual abstractions for.

x-ray shouldn't be that different from the other rays of light in its behavior in illuminating an object had our eyes had evolved to detect them. So they should be same.

”I don’t want to be human. I want to see gamma rays, I want to hear X-rays, and I want to smell dark matter. Do you see the absurdity of what I am? I can’t even express these things properly, because I have to—I have to conceptualize complex ideas in this stupid, limiting spoken language, but I know I want to reach out with something other than these prehensile paws, and feel the solar wind of a supernova flowing over me. I’m a machine, and I can know much more.

—John Cavil, Cylon Model Number One, Battlestar Galactica

The pictures we see of anything are the stuff around them.

Some photo-interactive boundary conditions we are near enough, and sensitive enough, to perceive directly. Some not.

Here’s what telescopes actually capture: https://www.eso.org/public/videos/eso0846j/

(And here is a long thread about it from 4 months back if anyone is interested: https://news.ycombinator.com/item?id=16480142)

Worth keeping in mind is that it is only slightly better than even odds this was actually an astrophysical neutrino.

Very much better than even odds.

We report the detection of a high-energy neutrino by IceCube and the multiwavelength/multi-instrument observations of a flaring γ-ray blazar, TXS 0506+056, which was found to be positionally coincident with the neutrino direction (16). Chance coincidence of the IceCube-170922A event with the flare of TXS 0506+056 is statistically disfavored at the level of 3σ in models evaluated below, associating neutrino and γ-ray production.

Which is to say 1:370

Supposing it was astrophysical, the chance coincidence is low yes, but:

> The muon-neutrino astrophysical spectrum, together with simulated data, was used to calculate the probability that a neutrino at the observed track energy and zenith angle in IceCube is of astrophysical origin. This probability, the so-called signalness of the event (14), was reported to be 56.5% (17).

Meaning there is about even odds this was not from outer space, but from a cosmic ray hitting the atmosphere, and we know cosmic rays point back at nothing in particular.

But does that probability take into account the coincidence of the putative source being lined up, or not?

No, that is purely the chance that they correctly identified the event as being signal, it doesn't take into account known sources.

Given that the background is basically isotropic, I doubt adding in a source catalogue will move the probability much.

You're saying there are blazars everywhere, such that no matter the trajectory, it would match to something? That doesn't sound right.

No, I'm saying cosmic rays come from anywhere (as the get deflected by magnetic fields) and when hitting the atmosphere they can create high energy neutrinos that can look like they are from space despite actually being from the atmosphere.

Could someone please ELI5 the distinction between blazars and quasars? I get that quasars are radio sources. But so are blazars, right? Is it that blazars are pointed right at us, whereas quasars aren't necessarily?

According to:

https://en.wikipedia.org/wiki/Quasar

In the 1980s, unified models were developed in which quasars were classified as a particular kind of active galaxy, and a consensus emerged that in many cases it is simply the viewing angle that distinguishes them from other active galaxies, such as blazars and radio galaxies.

..also...

A minority of quasars show strong radio emission, which is generated by jets of matter moving close to the speed of light. When viewed downward, these appear as blazars ...

To the best of my knowledge and interpretation they can be a type of "Quasar" but are really a type of galaxy with an active galactic nucleus (AGN) where their jets point towards Earth:

https://en.wikipedia.org/wiki/Blazar

A blazar is an active galactic nucleus with a relativistic jet (a jet composed of ionized matter traveling at nearly the speed of light) directed very nearly toward the Earth.

https://en.wikipedia.org/wiki/Active_galactic_nucleus#Types_...

Thanks. I did skim the Wikipedia articles, but wasn't left with a clear understanding.

But OK, I get that they're all galaxies with AGNs aka massive black holes. And that blazars are the ones with a jet pointed right at us.

But now I'm curious. When a jet is pointed right at us, we see visible, x-ray and gamma radiation, and relativistic particles. But is longer wavelength radiation also emitted mainly on the jet axis?

I'd be a complete fraud if I said I could answer that :)

Yeah, me too :)

But this is interesting: https://www.bu.edu/blazars/VLBAproject.html

I'm just as amazed that a place like the IceCube Neutrino Observatory could be built.

So it emits particles at near-light-speeds aimed towards us. Some questions (possibly stupid).

Are they still at near-light-speed when the get to us?

How can you detect something going so fast? Aren't there weird relativistic behaviors?

dickbar on top

dickbar on bottom

dickbars to the sides

https://outline.com/http://blogs.discovermagazine.com/crux/2...

Blazer?

http://en.wikipedia.org/wiki/Chevrolet_Blazer

While its gravitational density may approach a black hole, it's not an astronomical phenomenon.

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