How does the very low level interferometry allow us to image a black hole?




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The HD 163296 is representative of a typical protoplanetary disk viewed by the DSHARP collaboration. It has a central protoplanetary disk, external emission rings and empty spaces between them. There should be several planets in this system, and one can identify a strange artifact inside the ring located near the second circle, which can be a telltale sign of a disturbed planet. . The scale bar at the bottom right is 10 AU, which corresponds to a resolution of only a few milliarcseconds. This can only be done by VLBI.

S.M. Andrews et al. and the DSHARP collaboration, arXiv: 1812.04040

The Horizon Telescope of Events has accomplished that no other telescope or network of telescopes has ever achieved: directly imaging the event horizon of a black hole. A team of more than 200 scientists using data from eight independent telescope installations on five continents have come together to make this monumental triumph. Although many contributions and contributors deserve to be underlined, there is a fundamental physics technique on which everything depends: Very long interferometryor VLBI. Partisan of Patreon Ken Blackman wants to know how it works and how it allowed this remarkable feat, asking:

[The Event Horizon Telescope] use VLBI. So what is the interferometry and how was it used by [the Event Horizon Telescope]? It looks like it was a key ingredient in the production of the M87 image but I do not know how or why. Care to elucidate?

You are on Let's do it.

Any reflection telescope is based on the principle of the reflection of incoming light rays via a large primary mirror which focuses this light onto a point, where it is then decomposed into data and recorded or used to construct an image. This specific diagram illustrates the light paths for a Herschel-Lomonosov telescope system.

Eudjinnius, user of Wikimedia Commons

For a single telescope, everything is relatively simple. The light comes in the form of a series of parallel rays, all originating from the same distant source. The light hits the main mirror of the telescope and focuses on a single point. If you place an extra mirror (or set of mirrors) on the path of light, they will not change that story. they simply change where this light converges to a point.

All of these light rays arrive at the same end point at the same time, where they can then be combined into one image or saved as raw data for later processing in an image. This is the ultra-basic version of a telescope: the light comes from a source, focuses in a small area and is recorded.

Small section of the Karl Jansky Very Large Array, one of the largest and most powerful radio telescope networks in the world. Unless the individual antennas are properly synchronized together, they will not reach a resolution greater than that of a single antenna.

John Fowler

But what if you do not have a single telescope, but several telescopes that are networked in a kind of matrix? You might think that you could simply treat the problem in the same way and focus the light of each telescope as you would for a single-antenna telescope. The light would always arrive in parallel rays; each primary mirror would always focus this light on a single point; the light rays of each telescope arrive at the same time at the end point; all these data can then be collected and stored.

You can do it, of course. But that would only give you two independent images. You can combine them, but that would only average the data. It would be like watching your target with a single telescope at two different times and adding the data.

Once completed, the square kilometer chart will include a set of thousands of radio telescopes, capable of seeing farther into the Universe than any observatory that has measured any type of star or galaxy.

Project Development Office SKA and Swinburne Astronomy Productions

This does not help you with your big problem, which is that you need the essential enhanced resolution that comes with the use of a network of telescopes linked together by VLBI. When you combine several telescopes with the VLBI technique, you will get an image combining the light gathering power of individual satellite dishes, but (optimally) with the resolution of the distance between the antennas.

This technique has been used many times, not only for the imaging of a black hole, nor even with radio telescopes. In fact, the most spectacular example of VLBI may have been used by Large binocular telescope, which has two telescopes of 8 meters mounted together, behaving with the resolution of a telescope of ~ 23 meters. As a result, it can solve problems that no 8-meter antenna can solve, such as the eruption of volcanoes on Io while it undergoes an eclipse from another of the moons of Jupiter.

The occultation of the moon of Jupiter, Io, with its erupting volcanoes, Loki and Pelé, obscured by Europa, invisible in this infrared image. The large binocular telescope was able to do this through the technique of interferometry.

LBTO

To unlock this type of energy, you must be able to collect your observations at the same time. & Nbsp; The light signals that arrive on the telescopes arrive after slightly different light-path times, because of the variable distance, at the speed of light, the signal must travel from the source object to the various detectors / telescopes of the earth.

You must know the time of arrival of the signals at different telescope locations around the world to be able to combine them into a single image. It is only by combining data matching the simultaneous display of the same source that we will be able to achieve the maximum resolution that a network of telescopes is able to offer.

This diagram shows the location of all telescopes and their networks used in the observations of the M87 Event Horizon 2017 telescope. Only the South Pole telescope has not been able to image M87 because it is located in the wrong part of the Earth never to see the center of this galaxy. Each of these places is equipped with an atomic clock, among other amenities.

NRAO

To do this, we use practically atomic clocks. An atomic clock is located on each of the 8 locations on the globe where the Event Horizon telescope takes data, which allows us to keep the time necessary to obtain a few attosecond accuracies (10-18 s). It was also necessary to install specialized computer equipment (hardware and software) to enable correlation and synchronization of observations between the different stations of the world.

You must observe the same object at the same time and at the same frequency, while correcting problems like atmospheric noise with a correctly calibrated telescope. It is a demanding task in the workforce that requires enormous precision. But when you get there, the result is amazing.

The protoplanetary disk around the young star, HL Tauri, photographed by ALMA. The spaces in the disc indicate the presence of new planets. This system has been around for hundreds of millions of years and the planets are about to end. This resolution is only possible thanks to the use of VLBI by ALMA.

ALMA (ESO / NAOJ / NRAO)

The picture above may not have anything to do with a black hole, but it is actually one of the most famous images of the most powerful network of radio telescopes: ALMA. ALMA stands for Atacama Large Millimeter / Submillimeter Array. It consists of 66 independent radio antennas that can be adjusted to be spaced 150 meters by 16 kilometers.

The light collection power is simply determined by the surface of the individual dishes combined; it does not change. But the resolution that he can achieve is determined by the distance between the dishes. This is so that it can reach resolutions up to a few milliseconds or a millionth of a degree.

Atacama's large millimeter / submillimeter network (ALMA) is one of the most powerful radio telescopes in the world. These telescopes can measure the signatures of atoms, molecules and long-wave ions inaccessible to shorter telescopes like Hubble, but they can also measure the details of protoplanetary systems and, potentially, even foreign signals that even infrared telescopes can not see. This was the most important addition to the Horizon Event telescope.

ESO / C. Malin

But as impressive as ALMA is, the Event Horizon telescope goes even further. With baselines between stations approaching Earth's diameter – more than 10,000 km & nbsp; – It can solve objects as small as 15 micro-seconds of arc approximately. This incredible improvement in resolution allowed him to image the black hole event horizon (a thickness of 42 micro-seconds arc) at the center of the M87 galaxy.

The key to obtaining this image and to making these high-resolution observations in general is to synchronize each telescope with observations that coincide perfectly with time. For this to happen is simple from a conceptual point of view, but mandatory & nbsp;a monumental innovation put this into practice.

In VLBI, radio signals are recorded on each individual telescope before being sent to a central location. Each received data point is time stamped with an extremely accurate high frequency atomic clock, to help scientists get the timing of observations.

Public domain / User Wikipedia Rnt20

The main breakthrough came in 1958, when scientist Roger Jennison wrote a now famous paper: & nbsp; Phase-sensitive interferometer technique for Fourier transform measurement of spatial light distribution distributions of small angular extent. It sounds like a bite, but here's how you can understand it in a simple way.

  1. Imagine that you have three antennas (or radio telescopes) all connected together and separated by particular distances.
  2. These antennas will receive signals from a distant source, where the relative arrival times of the different signals can be calculated.
  3. When you mix the different signals, they interfere with each other, due to real effects and errors.
  4. What Jennison has developed – and what is still used today in the form of auto-calibration & nbsp; – is the technique to correctly combine real effects and ignore errors.

This is known today as opening synthesis, and the basic principle has remained the same for more than 60 years.

In April 2017, the 8 telescopes / telescope networks associated with the Event Horizon telescope pointed to Messier 87. Here's what a supermassive black hole looks like, where the horizon of events is clearly visible. Only through VLBI could we get the resolution needed to build an image like this.

Event Collaboration Horizon Telescope et al.

What is fantastic with this technique is that it can be applied in any range of wavelengths. At present, the Event Horizon telescope measures radio waves of a given frequency, but it could theoretically operate at a frequency three to five times higher. Since the resolution of your telescope depends on the number of waves that can be adapted to the diameter (or baseline) of the telescope, switching to higher frequencies results in longer wavelengths. short and higher resolution. We could get five times the resolution without needing to build a single new dish.

The first black hole may have arrived a few days ago, but we are already looking into the future. The first event horizon is really just the beginning. In addition to this, the Event Horizon telescope should one day be able to solve the characteristics of remote blazars and other bright radio sources, allowing us to understand them like never before. Welcome to the world of VLBI, where if you want a high resolution telescope, you just need to move the ones you have farther away from each other!


Send your questions to Ask Ethan at departwithabang to gmail dot com!

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The HD 163296 is representative of a typical protoplanetary disk viewed by the DSHARP collaboration. It has a central protoplanetary disk, external emission rings and empty spaces between them. There should be several planets in this system, and one can identify a strange artifact inside the ring located near the second circle, which can be a telltale sign of a disturbed planet. . The scale bar at the bottom right is 10 AU, which corresponds to a resolution of only a few milliarcseconds. This can only be done by VLBI.

S.M. Andrews et al. and the DSHARP collaboration, arXiv: 1812.04040

The Horizon Telescope of Events has accomplished that no other telescope or network of telescopes has ever done: directly imaging the event horizon of a black hole. A team of more than 200 scientists using data from eight independent telescope installations on five continents have come together to make this monumental triumph. Although many contributions and contributors deserve to be highlighted, there is a fundamental physics technique on which everything depends: very low level interferometry, or VLBI. Patreon supporter Ken Blackman wants to know how it works and how he has made this remarkable feat:

[The Event Horizon Telescope] use VLBI. So what is the interferometry and how was it used by [the Event Horizon Telescope]? It looks like it was a key ingredient in the production of the M87 image but I do not know how or why. Care to elucidate?

You are on Let's do it.

Any reflection telescope is based on the principle of the reflection of incoming light rays via a large primary mirror which focuses this light onto a point, where it is then decomposed into data and recorded or used to construct an image. This specific diagram illustrates the light paths for a Herschel-Lomonosov telescope system.

Eudjinnius, user of Wikimedia Commons

For a single telescope, everything is relatively simple. The light comes in the form of a series of parallel rays, all originating from the same distant source. The light hits the main mirror of the telescope and focuses on a single point. If you place an extra mirror (or set of mirrors) on the path of light, they will not change that story. they simply change where this light converges to a point.

All of these light rays arrive at the same end point at the same time, where they can then be combined into one image or saved as raw data for later processing in an image. This is the ultra-basic version of a telescope: the light comes from a source, focuses in a small area and is recorded.

Small section of the Karl Jansky Very Large Array, one of the largest and most powerful radio telescope networks in the world. Unless the individual antennas are properly synchronized together, they will not reach a resolution greater than that of a single antenna.

John Fowler

But what if you do not have a single telescope, but several telescopes that are networked in a kind of matrix? You might think that you could simply treat the problem in the same way and focus the light of each telescope as you would for a single-antenna telescope. The light would always arrive in parallel rays; each primary mirror would always focus this light on a single point; the light rays of each telescope arrive at the same time at the end point; all these data can then be collected and stored.

You can do it, of course. But that would only give you two independent images. You can combine them, but that would only average the data. It would be like watching your target with a single telescope at two different times and adding the data.

Once completed, the square kilometer chart will include a set of thousands of radio telescopes, capable of seeing farther into the Universe than any observatory that has measured any type of star or galaxy.

Project Development Office SKA and Swinburne Astronomy Productions

This does not help you with your big problem, which is that you need the essential enhanced resolution that comes with the use of a network of telescopes linked together by VLBI. When you combine several telescopes with the VLBI technique, you will get an image combining the light gathering power of individual satellite dishes, but (optimally) with the resolution of the distance between the antennas.

This technique has been used many times, not only for the imaging of a black hole, nor even with radio telescopes. In fact, the large binocular telescope, which has two 8-meter telescopes mounted together, behaves with the resolution of a telescope of about 23 meters, is perhaps the most spectacular example of VLBI. As a result, it can solve problems that no 8-meter antenna can solve, such as the eruption of volcanoes on Io while it undergoes an eclipse from another of the moons of Jupiter.

The occultation of the moon of Jupiter, Io, with its erupting volcanoes, Loki and Pelé, obscured by Europa, invisible in this infrared image. The large binocular telescope was able to do this through the technique of interferometry.

LBTO

To unlock this type of power, it is essential that you gather your observations at the same time. The light signals arriving on the telescopes arrive after slightly different light displacement times, due to the variable distance, at the speed of light, the signal to move from the source object to the various detectors / telescopes located Earth.

You must know the time of arrival of the signals at different telescope locations around the world to be able to combine them into a single image. It is only by combining data matching the simultaneous display of the same source that we will be able to achieve the maximum resolution that a network of telescopes is able to offer.

This diagram shows the location of all telescopes and their networks used in the observations of the M87 Event Horizon 2017 telescope. Only the South Pole telescope has not been able to image M87 because it is located in the wrong part of the Earth never to see the center of this galaxy. Each of these places is equipped with an atomic clock, among other amenities.

NRAO

To do this, we use practically atomic clocks. An atomic clock is located on each of the 8 locations on the globe where the Event Horizon telescope takes data, which allows us to keep the time necessary to obtain a few attosecond accuracies (10-18 s). It was also necessary to install specialized computer equipment (hardware and software) to enable correlation and synchronization of observations between the different stations of the world.

You must observe the same object at the same time and at the same frequency, while correcting problems like atmospheric noise with a correctly calibrated telescope. It is a demanding task in the workforce that requires enormous precision. But when you get there, the result is amazing.

The protoplanetary disk around the young star, HL Tauri, photographed by ALMA. The spaces in the disc indicate the presence of new planets. This system has been around for hundreds of millions of years and the planets are about to end. This resolution is only possible thanks to the use of VLBI by ALMA.

ALMA (ESO / NAOJ / NRAO)

The picture above may not have anything to do with a black hole, but it is actually one of the most famous images of the most powerful network of radio telescopes: ALMA. ALMA stands for Atacama Large Millimeter / Submillimeter Array. It consists of 66 independent radio antennas that can be adjusted to be spaced 150 meters by 16 kilometers.

The light collection power is simply determined by the surface of the individual dishes combined; it does not change. But the resolution that he can achieve is determined by the distance between the dishes. This is so that it can reach resolutions up to a few milliseconds or a millionth of a degree.

Atacama's large millimeter / submillimeter network (ALMA) is one of the most powerful radio telescopes in the world. These telescopes can measure the signatures of atoms, molecules and long-wave ions inaccessible to shorter telescopes like Hubble, but they can also measure the details of protoplanetary systems and, potentially, even foreign signals that even infrared telescopes can not see. This was the most important addition to the Horizon Event telescope.

ESO / C. Malin

But as impressive as ALMA is, the Event Horizon telescope goes even further. With baselines between stations approaching Earth's diameter – more than 10,000 km – it can solve objects as small as about 15 micro-seconds of arc. This incredible improvement in resolution allowed him to image the black hole event horizon (a thickness of 42 micro-seconds arc) at the center of the M87 galaxy.

The key to obtaining this image and to making these high-resolution observations in general is to synchronize each telescope with observations that coincide perfectly with time. To get there, the concept is simple, but it takes a monumental innovation to put it into practice.

In VLBI, radio signals are recorded on each individual telescope before being sent to a central location. Each received data point is time stamped with an extremely accurate high frequency atomic clock, to help scientists get the timing of observations.

Public domain / User Wikipedia Rnt20

The key breakthrough came in 1958, when scientist Roger Jennison wrote a now famous article: A phase-sensitive interferometer technique for measuring the Fourier transform of small angular extent spatial light distributions . It sounds like a bite, but here's how you can understand it in a simple way.

  1. Imagine that you have three antennas (or radio telescopes) all connected together and separated by particular distances.
  2. These antennas will receive signals from a distant source, where the relative arrival times of the different signals can be calculated.
  3. When you mix the different signals, they interfere with each other, due to real effects and errors.
  4. What Jennison has come up with – and what is still used today in the form of self-calibration – is the technique of properly combining real effects and ignoring errors.

This is what we call today the opening synthesis, and the basic principle has remained the same for more than 60 years.

In April 2017, the 8 telescopes / telescope networks associated with the Event Horizon telescope pointed to Messier 87. Here's what a supermassive black hole looks like, where the horizon of events is clearly visible. Only through VLBI could we get the resolution needed to build an image like this.

Event Collaboration Horizon Telescope et al.

What is fantastic with this technique is that it can be applied in any range of wavelengths. At present, the Event Horizon telescope measures radio waves of a given frequency, but it could theoretically operate at a frequency three to five times higher. Since the resolution of your telescope depends on the number of waves that can be adapted to the diameter (or base line) of the telescope, switching to higher frequencies results in shorter wavelengths and a higher resolution. We could get five times the resolution without needing to build a single new dish.

The first black hole may have arrived a few days ago, but we are already looking into the future. The first event horizon is really just the beginning. In addition to this, the Event Horizon telescope should one day be able to solve the characteristics of remote blazars and other bright radio sources, allowing us to understand them like never before. Welcome to the world of VLBI, where if you want a high resolution telescope, you just need to move the ones you have farther away from each other!


Send your Ask Ethan questions to startswithabang to gmail dot com!


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