Starship Asterisk*

Nitpicker wrote: ↑Thu Apr 11, 2019 11:43 am
Light that approaches a radius of about 2.5 or 2.6 times the radius of the event horizon, spirals inward and crosses the event horizon, never to be seen again. That's the explanation for the size of the shadow, as I understand it.

https://en.wikipedia.org/wiki/Photon_sphere wrote:
<<A photon sphere is a spherical area or region of space where gravity is so strong that photons are forced to travel in orbits. The radius of the photon sphere—which is also the lower bound for any stable orbit—is, for a Schwarzschild black hole:

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where r_s is the Schwarzschild radius (the radius of the event horizon).

As photons approach the event horizon of a black hole, those with the appropriate energy avoid being pulled into the black hole by traveling in a nearly tangential direction known as an exit cone. A photon on the boundary of this cone does not possess the energy to escape the gravity well of the black hole. Instead, it orbits the black hole. These orbits are rarely stable in the long term.

Within a photon sphere, it is possible to imagine a photon that begins at the back of your head, orbiting the black hole, only then to be intercepted by your eyes, allowing you to see the back of your head. There are no stable free fall orbits that exist within or cross the photon sphere. Any free fall orbit that crosses it from the outside spirals into the black hole. Any orbit that crosses it from the inside escapes to infinity. No unaccelerated orbit with a semi-major axis less than this distance is possible, but within the photon sphere, a constant acceleration will allow a spacecraft or probe to hover above the event horizon.

A rotating black hole has two photon spheres. As a black hole rotates, it drags space with it. The photon sphere that is closer to the black hole is moving in the same direction as the rotation, whereas the photon sphere further away is moving against it. The greater the angular velocity of the rotation of a black hole, the greater the distance between the two photon spheres. Since the black hole has an axis of rotation, this only holds true if approaching the black hole in the direction of the equator. If approaching at a different angle, such as one from the poles of the black hole to the equator, there is only one photon sphere. This is because approaching at this angle the possibility of traveling with or against the rotation does not exist.>>

RocketRon wrote: ↑Thu Apr 11, 2019 8:05 am There is some discussion on the BBC about the algorithm that was developed to achieve this,
and the gal behind it. With not enough detail to recreate this, so we will wait and see where that discussion leads.
If it took 3 years of analysing data, as it seems to be indicated, it would suggest its not so simple !! ?

guesto wrote: ↑Thu Apr 11, 2019 1:54 pm
Can anyone tell us if this image and the Hubble one showing the jet stream at about the 2 o'clock position, are taken at the same radial orientation? In other words, can you lay one on top of the other and they line up?

https://www.livescience.com/65200-black-hole-event-horizon-image-questions-remain.html wrote:

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3 Huge Questions the Black Hole Image Didn't Answer
By Rafi Letzter, Staff Writer | April 10, 2019 02:22pm ET

On the left, an image taken using the CHANDRA X-Ray Telescope at the same time as the Event Horizons Telescope made its picture shows a relatavistic jet crossing the Virga A galaxy. On the right is the image of the black hole shadow from the Event Horizons Telescope.

Credit: Credit: X-ray: NASA/CXC/Villanova University/J. Neilsen; Radio: Event Horizon Telescope Collaboration

guesto wrote: ↑Thu Apr 11, 2019 2:23 pm
Thanks neufer, but...

"Same time" yes. However, do they line up?

Also I should have asked about the scales. Same? Different by how much? etc.

Case wrote: ↑Thu Apr 11, 2019 5:42 am The ESO video called it “superheated gas and dust”. Are we seeing (the bright parts of) the accretion disk here? Does such a disk go all the way up to the event horizon?
Why is “the shadow” of the black hole not the same as event horizon?

eventhorizontelescope.org wrote:

Scientists have obtained the first image of a black hole, using Event Horizon Telescope observations of the center of the galaxy M87. The image shows a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the Sun.

Ann wrote: ↑Thu Apr 11, 2019 3:04 pm If I read the caption from eventhorizontelescope.org correctly, the luminous ring we are seeing is not (or not necessarily) the accretion disk around the black hole. Instead, we are seeing a small Einstein ring, not one encircling an entire galaxy as in the picture at right, but one encircling just the black hole of M87.

In both cases, the Einstein rings are caused by light being very strongly bent in the presence of very strong gravity.

Nitpicker wrote: ↑Thu Apr 11, 2019 7:34 am

Confused wrote: ↑Thu Apr 11, 2019 7:30 am The thing I don't hear anyone talking about is why they had to get a black hole from more than 50 million light-years. Why can't they get an image of the (or a) black hole in our galaxy? If astronomers are unable to get an image of a black hole in our galaxy then how can they be sure that the image is what they think it is?

In absolute terms, the BH at centre of (comparatively featureless) M87 is much larger than the BH at the centre of the dusty Milky Way, and I might guess M87 is less obscured by the bits of the Milky Way in between. The BHs are comparable in terms of angular size from Earth.

RocketRon wrote: ↑Thu Apr 11, 2019 9:06 am Bear in mind that this image was taken with radio telescopes, so 'light' doesn't come into it,
its radio signals that were being analysed.

One also wonders about the assumptions that were made about how radio waves operate around black holes and/or are generated,
that should provide further/future discussions for quite some time ?

Chris Peterson wrote: ↑Thu Apr 11, 2019 3:13 pm

Ann wrote: ↑Thu Apr 11, 2019 3:04 pm If I read the caption from eventhorizontelescope.org correctly, the luminous ring we are seeing is not (or not necessarily) the accretion disk around the black hole. Instead, we are seeing a small Einstein ring, not one encircling an entire galaxy as in the picture at right, but one encircling just the black hole of M87.

In both cases, the Einstein rings are caused by light being very strongly bent in the presence of very strong gravity.

The light (millimeter wavelength radiation) we are seeing is definitely from an accretion disk. It is distorted by the intense gravitational field around the black hole. Unlike an Einstein ring, it is not radiation from a distance source behind the galaxy.

Confused wrote: ↑Thu Apr 11, 2019 4:25 pm

RocketRon wrote: ↑Thu Apr 11, 2019 9:06 am Bear in mind that this image was taken with radio telescopes, so 'light' doesn't come into it,
its radio signals that were being analysed.

One also wonders about the assumptions that were made about how radio waves operate around black holes and/or are generated,
that should provide further/future discussions for quite some time ?

Just before noon in the Eastern timezone Mike Massimino in Fox News is saying that we are seeing light. Is he an authority on the subject or is Fox News using someone unqualified to speak on the subject?

Okay, now he is saying they used radio telescopes. I think he is confusing people. He should not have said we are seeing light, right?

Ann wrote: ↑Thu Apr 11, 2019 4:28 pm

Chris Peterson wrote: ↑Thu Apr 11, 2019 3:13 pm

Ann wrote: ↑Thu Apr 11, 2019 3:04 pm If I read the caption from eventhorizontelescope.org correctly, the luminous ring we are seeing is not (or not necessarily) the accretion disk around the black hole. Instead, we are seeing a small Einstein ring, not one encircling an entire galaxy as in the picture at right, but one encircling just the black hole of M87.

In both cases, the Einstein rings are caused by light being very strongly bent in the presence of very strong gravity.

The light (millimeter wavelength radiation) we are seeing is definitely from an accretion disk. It is distorted by the intense gravitational field around the black hole. Unlike an Einstein ring, it is not radiation from a distance source behind the galaxy.

Right. I can see that this is not an Einstein ring.

Isn't it possible, though, for light (or any other wavelengths from the electromagnetic spectrum) to get stuck in a loop around the even horizon of a black hole?

Psnarf wrote: ↑Thu Apr 11, 2019 6:11 pm Is this image the first proof that a black hole exists at the center of Messier 87 and perhaps most, if not all, galaxies?

FLPhotoCatcher wrote: ↑Thu Apr 11, 2019 7:07 pm What I don't understand (one of many, actually) is why do the radio observations need to be taken at practically the exact same time to be successfully combined? Doesn't the black hole look basically the same even a few hours later? And the radio waves detected at different radio dishes are not necessarily from the same sources.

daddyo wrote: ↑Thu Apr 11, 2019 5:42 am It’s claimed the telescope array has enough resolution to resolve writing on a coin at the distance between New York and Los Angeles. That’s crazy. I wonder how they collimated such a device. Awesome work. They will have a career in resolving other objects out there.

Martin wrote: ↑Thu Apr 11, 2019 7:19 pm

daddyo wrote: ↑Thu Apr 11, 2019 5:42 am It’s claimed the telescope array has enough resolution to resolve writing on a coin at the distance between New York and Los Angeles. That’s crazy. I wonder how they collimated such a device. Awesome work. They will have a career in resolving other objects out there.

Wonder no more. The answer is algorithm, Computational science. And a overdue standing ovation to the woman who's effort made it all possible today: Katie Bouman.