Event Horizon Telescope

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Individual observatories of the Event Horizon Telescope

The Event Horizon Telescope ( EHT , German  E reignis h orizont t eleskop ) is a network of radio telescopes to examine far-away black holes using Very Long Baseline Interferometry (VLBI) . Radio telescopes around the world pick up signals that are caused by the black holes. The resulting series of measurements are saved (the data volumes are too large for Internet transmission) and taken to computer centers (such as the VLBI correlator at the Max Planck Institute for Radio Astronomy in Bonn ) on data carriers ( racks with hard drives ) , where they are evaluated . The large distance between the telescopes on the earth's surface enables an angular resolution that is far higher than that of the individual radio telescopes.

The first two targets of the network are the supermassive black hole Sagittarius A * in the center of the Milky Way and the black hole in the center of the giant elliptical galaxy M87 . The aim is to check predictions of the general theory of relativity and to find explanations for the formation of the extremely energetic jets of supermassive black holes.

The first suggestions how the event horizon could be observed with interconnected radio telescopes were made in 2000 by Heino Falcke , Fulvio Melia and Eric Agol . The plans for the EHT were concretized at a meeting of radio astronomers in January 2012 in Tucson ("Bringing Black Holes into Focus: The Event Horizon Telescope"). Observation takes place at a wavelength of 1.3 mm (230 GHz); Observations at even shorter wavelengths (0.87 mm, corresponding to 345 GHz) are in preparation in 2019. The key element to the success of the EHT is that the ALMA radio interferometer was made VLBI-capable at 230 GHz in 2016 (also in the 86 GHz band, corresponding to 3.5 mm wavelength, in the Global Millimeter VLBI Array , GMVA). At the beginning of April 2017 it took part for the first time in VLBI observations at 86 GHz (GMVA) and 230 GHz (EHT), which improved the resolution in north-south direction by a factor of three and the sensitivity significantly.

Shep Doeleman has been the director of the EHT since 2017 . The chairman of the EHT board is Anton Zensus , the scientific advisory board is headed by Heino Falcke . The EHT cooperation was awarded the Breakthrough Prize in Fundamental Physics and the Albert Einstein Medal (both for 2020).

Black hole in galaxy M87

First published representation of the "shadow" and the accretion inflows of a black hole , calculated from images of the Event Horizon telescope (core of the galaxy Messier 87 )
Rear of the 15-meter James Clerk Maxwell telescope

On April 10, 2019, the first high-resolution images of the active core of the galaxy M87 were presented to the public. It was the end result of months of analysis with complex image processing algorithms and the exclusion of interference effects. M87 is 55 million light-years from Earth, and the black hole at its center has a mass that was estimated to be 6.6 billion solar masses prior to the now available observation with the EHT. For the first time, the accretion flows of heated matter around a black hole, which are distorted in a ring by gravity, were shown . The ring shown has a diameter of 42 ± 3 micro- arcseconds and a width of less than 20 micro-arcseconds. The inner edge of the ring can be identified from the comparison with various computer simulations with the so-called shadow of the black hole. Shadow is the gravitationally distorted projection of the area from which no light can escape and which is limited by the photon orbit on which the captured light orbits the black hole and can either escape due to interference or is absorbed by the black hole. The black hole rotates clockwise when viewed from above, as in the published images. The bright spots at the lower edge of the ring can be explained by an axis of rotation inclined by 17 to 18 degrees to the viewer's line of sight and relativistic beaming in the direction of the observer. The Schwarzschild radius, which is a characteristic variable for the event horizon, is 4 to 7 micro-arc seconds, the dark area in the picture corresponds to the so-called shadow of the black hole, which results from the gravitational lensing effects of the photon emissions in the immediate vicinity of the black hole. It is up to five times larger than the event horizon. The calculated images show very good agreement with simulations based on the general theory of relativity and exceeded expectations and surprised participating scientists such as Anton Zensus , the director of the Max Planck Institute for Radio Astronomy in Bonn .

A direct connection to the jet of M 87 is not evident from the recordings. Due to the inclination of the axis of rotation to the line of sight and relativistic effects, only one of the two jets of M 87 can be seen optically.

Many statements result from the comparison of the images with computer simulations (carried out by the group of Luciano Rezzolla from the University of Frankfurt), but due to the distortion caused by the strong gravity, the conclusions about the underlying scenarios are not always clear - for example, a similar picture would result if one looks at the edge of a radiating plasma disk around the black hole, since the top and bottom would be visible at the same time due to the space-time curvature. The comparisons are sufficient to estimate the mass of the black hole at 6.5 ± 0.7 billion solar masses, but not to determine the angular momentum. With a rotating black hole, the shape of the event horizon changes ( Kerr metric ), but the deviation is only around four percent and depends on the viewing angle. A naked singularity can be excluded because the shadow would be smaller and significantly more asymmetrical.

Eight telescopes were involved in the creation of the images (a total of four each on one observation day) over four days in April 2017. The eight telescopes were distributed around the world: in Arizona (SMT, Submillimeter Telescope ), Chile ( Atacama Large Millimeter / submillimeter Array (Alma) and Atacama Pathfinder Experiment , Apex), Hawaii ( Submillimeter Array , SMA, James Clerk Maxwell Telescope , JCMT), Mexico ( Large Millimeter Telescope , LMT), Antarctica at the South Pole ( South Pole Telescope ) and Spain ( Pico del Veleta in Sierra Nevada, the 30 m IRAM Telescope , PV). The effective resolution of the telescope, which results from the interconnection of the individual telescopes, corresponds to the furthest distance between the observation stations (11,000 km); but not the light collection power. This only corresponds to the sum of the telescopes involved. The angular resolution corresponds to the resolution of a tennis ball on the moon when observed from the earth. The EHT network has now been expanded. The very extensive data (many petabytes, each of the eight telescopes delivered around 350 terabytes a day), the physical transport of which posed a particular problem, for example from Antarctica, then had to be compared precisely in terms of time and telescope alignment. The data was evaluated at the Max Planck Institute for Radio Astronomy and the MIT Haystack Observatory and dragged on for two years, not only because of the composition of the data from the various telescopes, but also because the scientists involved wanted to make sure that they would at the end of the complex procedure of imaging really had a direct image of a black hole in front of them. Over 200 scientists from 20 nations and 59 institutions took part. On the four observation days on April 5, 6, 10 and 11, 2017, there was a window of good weather on all eight stations.

At the same time, images of Sagittarius A * , the supermassive black hole in the center of the Milky Way, were created, which have since been further improved. This appears to be about the same size (although at 26,000 light years it is clearly - about a thousand times - closer, the black hole in M ​​87 is about a thousand times heavier), but it is more dynamic and the images are therefore more blurred. The matter in the immediate vicinity circulates with Sagittarius A every few minutes and not in a few days as with M 87. The pictures of Sagittarius A are also to be presented to the public soon (as of April 2019). In the images presented so far, no shadow can be seen, but they are still being corrected for scattering effects in the interstellar space between Earth and Sagittarius A.

At present (2019) only the shadows of the black holes of M87 and our Milky Way are big enough to be observed.

X-ray image of Sagittarius A * and two light echoes (marked) from a previous explosion

Participating institutions

The participating institutions include:

literature

  • Event Horizon Telescope Collaboration: First M87 Event Horizon Telescope Results , Astrophysical Journal Letters:
    • I: The Shadow of the Supermassive Black Hole, Volume 875, 2019, L1, Arxiv
    • II: Array and Instrumentation, Volume 875, 2019, L 2, Arxiv
    • III: Data Processing and Calibration, Volume 875, 2019, L 3, Arxiv
    • IV: Imaging the Central Supermassive Black Hole, Volume 875, 2019, L 4, Arxiv
    • V: Physical Origin of the Asymmetric Ring, Volume 875, 2019, L 5, Arxiv
    • VI. The Shadow and Mass of the Central Black Hole, Volume 875, 2019, L6, Arxiv
  • Oliver Porth et al. a .: The Event Horizon General Relativistic Magnetohydrodynamic Code Comparison Project , Arxiv 2019
  • Vincent Fish et al. a. (Event Horizon Telescope Collaboration): Observing --- and Imaging --- Active Galactic Nuclei with the Event Horizon Telescope , Galaxies, Volume 4, 2016, Arxiv 2016
  • D. Psaltis, S. Doeleman: How do you measure a black hole? In: Spektrum der Wissenschaft 2/16, Spektrum der Wissenschaft Verlagsgesellschaft , Heidelberg 2016, ISSN  0170-2971
  • YES census u. a .: A sharp look at black holes , press release from the Max Planck Institute for Radio Astronomy (April 21, 2015)

Web links

Individual evidence

  1. ↑ a b Davide Castelvecchi: How to hunt for a black hole with a telescope the size of Earth . In: Nature . tape 543 , no. 7646 , March 23, 2017, p. 478-480 , doi : 10.1038 / 543478a .
  2. ↑ a b Kazunori Akiyama u. a. (Event Horizon Telescope Collaboration): First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole, Astroph. J. Letters, April 10, 2019, IOPScience
  3. ^ Falcke, Melia, Agol: Viewing the Shadow of the Black Hole at the Galactic Center , Astroph. J. Letters, Volume 528, 2000, p. 13, bibcode : 2000ApJ ... 528L..13F , doi: 10.1086 / 312423 .
  4. ↑ Moving towards higher observing frequencies , EHT, accessed on January 14, 2020
  5. ↑ Sara Issaoun et al .: The size, shape, and Scattering of Sagittarius A * at 86 GHz: First VLBI with ALMA. ApJ, 2019, doi: 10.3847 / 1538-4357 / aaf732 , arXiv: 1901.06226 .
  6. ^ The Event Horizon Telescope Collaboration et al .: First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole. 2019 ApJL 875 L1 ' doi: 10.3847 / 2041-8213 / ab0ec7 .
  7. ↑ European Commission: Breakthrough discovery in astronomy: press conference. April 10, 2019, accessed April 10, 2019 .
  8. ↑ Frank Wunderlich-Pfeiffer: No photo of a black hole. In: Golem.de . April 19, 2019. Retrieved April 19, 2019 .
  9. ^ The Event Horizon Telescope Collaboration: First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole . The Astrophysical Journal Letters, April 10, 2019.
  10. ^ Deep inside M 87 , MPI Radioastronomy, April 20, 2017
  11. ↑ a b Sybille Anderl, Thiemo Heeg, Tor zur Hölle, Frankfurter Allgemeine Woche, No. 16, April 12, 2019, p. 60
  12. ↑ Ulf von Rauchhaupt, It's not a naked singularity, Frankfurter Allgemeine Sonntagszeitung, April 14, 2019, p. 57
  13. ↑ Shep Doeleman: Focus on the First Event Horizon Telescope Results , Astroph. J. Letters, April 2019
  14. ↑ Korey Haynes, Event Horizon Telescope releases first ever black hole image , Astronomy.com, April 10, 2019
  15. ↑ Johann Grolle, View into Nowhere, Der Spiegel, No. 16, April 13, 2004, pp. 94-103, here pp. 96f
  16. ^ Lifting the veil around the black hole in the center of our Milky Way , MPG for Radio Astronomy, January 21, 2019
  17. ↑ Ulf von Rauchhaupt, It's not a naked singularity, Frankfurter Allgemeine Sonntagszeitung, April 14, 2019, p. 56
  18. ↑ Collaborators. (No longer available online.) In: eventhorizontelescope.org. Archived from the original on April 15, 2017 ; accessed on March 27, 2017 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / eventhorizontelescope.org