Conveners
Radio Astronomy from Space: Block 1
- Yuri Kovalev (Lebedev Physical Institute)
- Michael Johnson (Center for Astrophysics | Harvard & Smithsonian)
Radio Astronomy from Space: Block 2
- Michael Johnson (Center for Astrophysics | Harvard & Smithsonian)
- Yuri Kovalev (Lebedev Physical Institute)
Description
Over the past century, radio astronomy has played a central role in experimental studies of General Relativity. Key milestones include measurement of the Shapiro time delay, discovery of cosmic background radiation, detection of gravitational waves using binary pulsars, discovery of superluminal motion in quasars, and the first image of a black hole using the EHT. Radio astronomy in space offers key advantages: WMAP and Planck revolutionized modern observational cosmology, while VSOP and RadioAstron achieved the sharpest resolution in the history of astronomy.
This parallel session will be devoted to recent results and plans for future space missions that target breakthroughs in experimental relativity using radio observations. The plans include high-resolution studies of the supermassive black holes Sgr A and M87 using a space-enhanced EHT, and cosmological studies using Lunar ultra-long wavelength radio telescopes.
In 2017, the Event Horizon Telescope (EHT) observed the supermassive black hole M 87* at the center of the giant elliptical galaxy Messier 87 using very-long baseline interferometry between a global network of radio telescopes. Operating at a high radio frequency of 230 GHz, EHT enables imaging of the optically thin emission region in the immediate vicinity of the event horizon of M 87*,...
In 2017, the Event Horizon Telescope (EHT) observed the black hole at the center of the giant elliptical galaxy, Messier 87 using very-long baseline interferometry between a global network of radio telescopes. The resulting linearly polarized images of the accretion flow near the horizon of the black hole (M 87*) show resolved polarized structure with a spiral pattern in the electric vector...
The photon ring is a narrow ring-shaped feature, predicted by General Relativity but not yet observed, that appears on images of sources near a black hole. It is caused by extreme bending of light within a few Schwarzschild radii of the event horizon and provides a direct probe of the unstable bound photon orbits of the Kerr geometry. The precise shape of the observable photon ring is...
The first imaging of the super massive black hole in M87 by the Event Horizon Telescope (EHT) has marked the beginning of a new era in black hole research that explores the properties through direct image observations. In particular, polarimetric images of the vicinity of black holes have attracted much attention because they reflect the magnetic field structure, which plays a key role in the...
Making a high resolution image of a supermassive black hole shadow is a direct method to verify the theory of general relativity at extreme gravity conditions. Very Long Baseline Interferometry (VLBI) observations at millimeter/sub-millimeter wavelengths can provide just provide angular resolution sufficient to start resolving supermassive black holes, located in Sgr A* and M87. Recent VLBI...
Very long baseline interferometry (VLBI) probes cosmic phenomena at the highest angular resolution in astronomy, with the present record set at about 10 microsecond of arc. This record is achieved in space VLBI (SVLBI) observations of the Russian-led RadioAstron mission which combined a worldwide array of radio telescopes with a 10-m antenna in orbit around the Earth. Continuing on the path of...
With the advent of the Event Horizon Telescope, the study of multiply lensed images of emitting material about black holes has become a reality. The direct detection of a bright, ring-like structure in horizon-resolving images of M87* is a striking validation of general relativity. However, this success raises a singular difficulty: the angular size and shape of these rings are potentially...
Simulated images of a black hole surrounded by optically thin emission typically display two main features: a central brightness depression and a narrow, bright "photon ring" consisting of strongly lensed images superposed on top of the direct emission. The photon ring closely tracks a theoretical curve on the image plane corresponding to light rays that asymptote to unstably bound photon...
The shadow around the supermassive black hole in M87 was reconstructed in 2019 based on its observations with the Event Horizon Telescope in 2017. Recently polarization map for the M87* shadow was presented. We discuss opportunities to evaluate parameters of alternative theories of gravity with shadow observations, in particular, a tidal charge could be estimated from these observations.
Black hole images are dominated by a "photon ring," a ring of light with universal properties that are completely governed by general relativity. This talk will discuss the univesal features of polarimetric images of black holes. In particular, the photon ring exhibits a self-similar pattern of polarization that encodes the black hole spin. The corresponding polarimetric signatures on long...
The Event Horizon Telescope (EHT) has imaged the shadow of the supermassive black hole in M87 and aims to image the Galactic Center black hole Sagittarius A (Sgr A) as well. As a ground-based VLBI array, the resolution of the current EHT is limited by the size of the Earth and the maximum attainable observing frequency, which is set by the severity of tropospheric corruptions beyond...
In 2019, the Event Horizon Telescope published the first image of a black hole, paving the way for future efforts to improve our understanding of emission around compact objects. However, many of the most prominent and unexpected effects of black holes on their images are only visible at extremely fine resolutions. To analyze these features, I will describe an approach to adaptive ray-tracing...
The highly-redshifted 21 cm line of neutral hydrogen holds great promise for cosmology. Observing this signal, however, is exceedingly challenging. Experiments must contend with the signal's inherent faintness, overwhelmingly bright astrophysical foregrounds, human-generated radio interference, and the Earth's own ionosphere. And, these challenges are all exacerbated for experiments looking...
