APOD: The Galaxy, the Jet, and a Famous... (2021 Apr 15)

[APOD Robot]

The Galaxy, the Jet, and a Famous Black Hole

Explanation: Bright elliptical galaxy Messier 87 (M87) is home to the supermassive black hole captured by planet Earth's Event Horizon Telescope in the first ever image of a black hole. Giant of the Virgo galaxy cluster about 55 million light-years away, M87 is the large galaxy rendered in blue hues in this infrared image from the Spitzer Space telescope. Though M87 appears mostly featureless and cloud-like, the Spitzer image does record details of relativistic jets blasting from the galaxy's central region. Shown in the inset at top right, the jets themselves span thousands of light-years. The brighter jet seen on the right is approaching and close to our line of sight. Opposite, the shock created by the otherwise unseen receding jet lights up a fainter arc of material. Inset at bottom right, the historic black hole image is shown in context, at the center of giant galaxy and relativistic jets. Completely unresolved in the Spitzer image, the supermassive black hole surrounded by infalling material is the source of enormous energy driving the relativistic jets from the center of active galaxy M87.

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[bystander]

viewtopic.php?t=39338#p291859
viewtopic.php?t=41587#p312511

[Ann]

viewtopic.php?t=39338#p291859
viewtopic.php?t=41587#p312511

Thanks, bystander! I'll add two picture and a bit of the captions.

Polarized light in the accretion disk of M87. Photo: Event Horizon Telescope Collaboration.

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EHT via ESO wrote:

The Event Horizon Telescope (EHT) collaboration, who produced the first ever image of a black hole, has today revealed a new view of the massive object at the centre of the Messier 87 (M87) galaxy: how it looks in polarised light. This is the first time astronomers have been able to measure polarisation, a signature of magnetic fields, this close to the edge of a black hole. The observations are key to explaining how the M87 galaxy, located 55 million light-years away, is able to launch energetic jets from its core.
...
The observations provide new information about the structure of the magnetic fields just outside the black hole. The team found that only theoretical models featuring strongly magnetised gas can explain what they are seeing at the event horizon.

“The observations suggest that the magnetic fields at the black hole’s edge are strong enough to push back on the hot gas and help it resist gravity’s pull. Only the gas that slips through the field can spiral inwards to the event horizon,” explains Jason Dexter, Assistant Professor at the University of Colorado Boulder, US, and Coordinator of the EHT Theory Working Group.

This wide-field image of the galaxy M87 was taken by NASA's Spitzer Space Telescope. The top inset shows a close-up of two shockwaves, created by a jet emanating from the galaxy’s supermassive black hole. The Event Horizon Telescope recently took a close-up image of the silhouette of that black hole, show in the second inset. Credits: NASA/JPL-Caltech/Event Horizon Telescope Collaboration.

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Nasa.gov. wrote:

This image from NASA's Spitzer Space Telescope shows the entire M87 galaxy in infrared light. The EHT image, by contrast, relied on light in radio wavelengths and showed the black hole's shadow against the backdrop of high-energy material around it.

The black hole of M87 emits two jets in opposite directions.

When the particles in the jet impact the interstellar medium (the sparse material filling the space between stars in M87), they create a shockwave that radiates in infrared and radio wavelengths of light but not visible light. In the Spitzer image, the shockwave is more prominent than the jet itself.
...
Infrared light at wavelengths of 3.6 and 4.5 microns are rendered in blue and green, showing the distribution of stars, while dust features that glow brightly at 8.0 microns are shown in red. The image was taken during Spitzer's initial "cold" mission.

So in the Spitzer image, blue means stars and red means dust. We can see that there is little dust in this area, but the shock fronts at the ends of the jets are dusty. A few dusty (and therefore red-looking) galaxies can be seen in the background.

Ann

[Knight of Clear Skies]

Imagine being the first astronomer on a world in M87 to realise that the orbit of your star system will take it through the jet...

[madtom1999]

We appear to be looking down on the accretion disk and yet the jets seem to be heading in the wrong direction for that to be true.

[RocketRon]

Never let the facts get in the way of a good story !?

Some of these 'images' have been produced by a vast amount of data processing.
It would be interesting to see what sort of safeguards have been put in place for the processing not to be self fulfilling ?

[VictorBorun]

We appear to be looking down on the accretion disk and yet the jets seem to be heading in the wrong direction for that to be true.

Here's my attempt to 3d-convert the radiowave pic of the clouds at the M87 jet-ends
Here's my attempt to 3d-convert the IR pic of the clouds at the M87 jet-ends
I used Spitzer's pic at wiki

[RocketRon]

Imagine being the first astronomer on a world in M87 to realise that the orbit of your star system will take it through the jet...

If those same circumstances and jet were in the centre of the Milky Way*,
how long before planet Earth would be affected though. ?

* and indeed could be, if we had a clearer view ??

What life threatening properties do such jets contain ??
We have a magnetic shield for such contingencies, would we even be affected. ?

"Milliways, better known as the Restaurant at the End of the Universe, is a five star restaurant situated at the
end of time and matter. Its main attraction is allowing diners to view a Gnab Gib, before desserts are served."
Credits -backwards - to Douglas Adams.

[Ann]

Imagine being the first astronomer on a world in M87 to realise that the orbit of your star system will take it through the jet...

Click to play embedded YouTube video.

It could have been even worse. We could have been living in the companion galaxy of the radio galaxy 3C 321, which blasts its neighbor galaxy with its terrific jet.


Ann

[Chris Peterson]

Imagine being the first astronomer on a world in M87 to realise that the orbit of your star system will take it through the jet...

This is not a very active black hole, and the relativistic jets are quite small, just a few thousand light years. It is unlikely that any stars that close to the center of M87 would be able to support stable enough planetary systems to allow for complex life to form. So I doubt that there are any astronomers out there who could make this determination.

[Chris Peterson]

We appear to be looking down on the accretion disk and yet the jets seem to be heading in the wrong direction for that to be true.

We are seeing the jet from one side only, and it is directed more or less towards us. And between the resolution of the radio image and the various gravitational distortions, it is difficult to determine visually just what the angle of the accretion disk is to us. And finally, the jets do not need to be perfectly perpendicular to the disk. They are only understood to be approximately so.

[Chris Peterson]

Never let the facts get in the way of a good story !?

Some of these 'images' have been produced by a vast amount of data processing.
It would be interesting to see what sort of safeguards have been put in place for the processing not to be self fulfilling ?

The Spitzer image is processed no differently from any astronomical image. The black hole image is constructed using the same math used for all interferometric radio telescope imagery (a lot of clever work went into optimizing the processing, but the math is still the same).

So... nothing extraordinary here.

[neufer]

NASA simulated view from outside the horizon of a Schwarzschild black hole lit by a thin accretion disk.

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We appear to be looking down on the accretion disk and yet the jets seem to be heading in the wrong direction for that to be true.

We appear to be looking on an accretion disk "mirage"
that is not incompatible with the direction of the jets.

Some of these 'images' have been produced by a vast amount of data processing. It would be interesting to see what sort of safeguards have been put in place for the processing not to be self fulfilling ?

Confirmation bias is always a risk but you do the best you can.

[neufer]

Greta Thunberg

---

Imagine being the first astronomer on a world in M87 to realise
that the orbit of your star system will take it through the jet...

Imagine being a climatologist/ecologist on our own world realizing
that he/she will live long enough to experience the Anthropocene.

[Chris Peterson]

Some of these 'images' have been produced by a vast amount of data processing. It would be interesting to see what sort of safeguards have been put in place for the processing not to be self fulfilling ?

Confirmation bias is always a risk but you do the best you can.

Confirmation bias may need to be guarded against to some degree in building the models that simulate black hole appearance. But in this case, there seems to be little opportunity for bias in processing and displaying the actual data. AFAIK the processing involved is deterministic and has no free parameters (or highly constrained parameters).

[shaileshs]

I wonder - What's that bright light circular object seen at the center (where black hole is suggested) in base image which seems to have disappeared in inset at top right ? What was it? Where did it go? Why?

[neufer]

I wonder - What's that bright light circular object seen at the center (where black hole is suggested) in base image which seems to have disappeared in inset at top right ? What was it? Where did it go? Why?

The central bright spot is from a visible or near infrared image such as seen in HST images:

• https://www.nasa.gov/feature/goddard/2017/messier-87

The other images are longer wavelength far infrared or radio.

[Fred the Cat]

Black holes have conjured my brain to imagine them as unique objects. Perhaps the leftover remnants stripped of hadrons and leptons?

Although way beyond the scope of my understanding, the conclusion of this article begins to shed light on jet formation.

[orin stepanek]

Looks good! !

[alter-ego]

Some of these 'images' have been produced by a vast amount of data processing. It would be interesting to see what sort of safeguards have been put in place for the processing not to be self fulfilling ?

Confirmation bias is always a risk but you do the best you can.

Confirmation bias may need to be guarded against to some degree in building the models that simulate black hole appearance. But in this case, there seems to be little opportunity for bias in processing and displaying the actual data. AFAIK the processing involved is deterministic and has no free parameters (or highly constrained parameters).

Reduction and display is an involved process. The paths to biased processing are numerous. As you said, independent image reduction was done independently from BH models, but image corroboration with model(s) was an important in the process. In addition, data from the 8 EHT sites covering multiple days had to be processed. From these papers, the image generation was far from deterministic.

5. Images and Features
We reconstructed images from the calibrated EHT visibilities, which provide results that are independent of models (Paper IV).However, there are two major challenges in reconstructing images from EHT data. First, EHT baselines sample a limited range of spatial frequencies, corresponding to angular scales between 25 and 160 μas. Because the (u, v) plane is only sparsely sampled (Figure 2), the inverse problem is under-constrained. Second, the measured visibilities lack absolute phase calibration and can have large amplitude calibration uncertainties.

To address these challenges, imaging algorithms incorporate additional assumptions and constraints that are designed to produce images that are physically plausible (e.g., positive and compact) or conservative (e.g., smooth), while remaining consistent with the data. We explored two classes of algorithms for reconstructing images from EHT data. The first class of algorithms is the traditional CLEAN approach used in radio interferometry (e.g., Högbom 1974; Clark 1980). CLEAN is an inverse-modeling approach that deconvolves the interferometer point-spread function from the Fourier-transformed visibilities. When applying CLEAN, it is necessary to iteratively self-calibrate the data between rounds of imaging to solve for time-variable phase and amplitude errors in the data. The second class of algorithms is the so-called regularized maximum likelihood (RML; e.g., Narayan & Nityananda 1986; Wiaux et al. 2009; Thiébaut 2013). RML is a forward-modeling approach that searches for an image that is not only consistent with the observed data but also favors specified image properties (e.g., smoothness or compactness). As with CLEAN, RML methods typically iterate between imaging and self-calibration, although they can also be used to image directly on robust closure quantities immune to station-based calibration errors. RML methods have been extensively developed for the EHT (e.g., Honma et al. 2014; Bouman et al. 2016; Akiyama et al. 2017; Chael et al. 2018b; see also Paper IV).

Every imaging algorithm has a variety of free parameters that can significantly affect the final image. We adopted a two-stage imaging approach to control and evaluate biases in the reconstructions from our choices of these parameters. In the first stage, four teams worked independently to reconstruct the first EHT images of M87* using an early engineering data release. The teams worked without interaction to minimize shared bias, yet each produced an image with a similar prominent feature: a ring of diameter ~38–44 μas with enhanced brightness to the south (see Figure 4 in Paper IV).

In the second imaging stage, we developed three imaging pipelines, each using a different software package and associated methodology. Each pipeline surveyed a range of imaging parameters, producing between ~103 and 104 images from different parameter combinations. We determined a "Top-Set" of parameter combinations that both produced images of M87* that were consistent with the observed data and that reconstructed accurate images from synthetic data sets corresponding to four known geometric models (ring, crescent, filled disk, and asymmetric double source). For all pipelines, the Top-Set images showed an asymmetric ring with a diameter of ~40 μas, with differences arising primarily in the effective angular resolutions achieved by different methods.

For each pipeline, we determined the single combination of fiducial imaging parameters out of the Top-Set that performed best across all the synthetic data sets and for each associated imaging methodology (see Figure 11 in Paper IV). Because the angular resolutions of the reconstructed images vary among the pipelines, we blurred each image with a circular Gaussian to a common, conservative angular resolution of 20 μas. The top part of Figure 3 shows an image of M87* on April 11 obtained by averaging the three pipelines' blurred fiducial images. The image is dominated by a ring with an asymmetric azimuthal profile that is oriented at a position angle ~170° east of north. Although the measured position angle increases by ~20° between the first two days and the last two days, the image features are broadly consistent across the different imaging methods and across all four observing days. This is shown in the bottom part of Figure 3, which reports the images on different days (see also Figure 15 in Paper IV). These results are also consistent with those obtained from visibility-domain fitting of geometric and general-relativistic magnetohydrodynamics (GRMHD) models (Paper VI).

[Knight of Clear Skies]

Imagine being the first astronomer on a world in M87 to realise that the orbit of your star system will take it through the jet...

This is not a very active black hole, and the relativistic jets are quite small, just a few thousand light years. It is unlikely that any stars that close to the center of M87 would be able to support stable enough planetary systems to allow for complex life to form. So I doubt that there are any astronomers out there who could make this determination.

I think you're making quite a lot of assumptions there, the biggest one being time. Over hundreds of millions of years a very large number of star systems will pass through the jet, and would be in its path for thousands of years. I don't know how to estimate how much reach the jet has, at what distance it could erode a planetary atmosphere, but I'd have thought a rough back-of-the-envelope calculation should be possible.

Many stars systems in M87 will be very old, it's the result of multiple mergers. Some will have elliptical orbits that take them close to the core regions, they did not necessarily form there.

In terms of the planetary formation, our very limited survey of other systems has turned up a lot of surprises so far. I'd be cautious about drawing many conclusions here. And when it comes to life the picture is even less clear, we can't say whether it is common or rare. We have a few clues, life appeared early in Earth's history but complex life took a very long time to develop, once the atmosphere had been supercharged with oxygen. This hints of a universe where life is fairly common but complex life is rare. But drawing conclusions from a sample size of one is the Gaia of all observational biases.

[Knight of Clear Skies]

Imagine being the first astronomer on a world in M87 to realise
that the orbit of your star system will take it through the jet...

Imagine being a climatologist/ecologist on our own world realizing
that he/she will live long enough to experience the Anthropocene.

Yes, sadly we don't have to look far afield to see potential catastrophe.