![]() If you measure how long the dip lasts, the researchers say, you can estimate the size and shape of the shadow cast by the black hole’s event horizon, the point of no exit, where nothing escapes, not even light. This subtle dimming can last from a few hours to a few days, depending on how massive the black holes, and how closely entwined their orbits. The lensing effect is well known, but what the researchers discovered here was a hidden signal: a distinctive dip in brightness corresponding to the “shadow” of the black hole in back. From this sideways vantage point, as one black hole passes in front of the other, you should be able to see a bright flash of light as the glowing ring of the black hole farther away is magnified by the black hole closest to you, a phenomenon known as gravitational lensing. Second, you need to be looking at the pair at a nearly side-on angle. First, you need a pair of supermassive black holes in the throes of merging. Outlined in complementary studies in Physical Review Letters and Physical Review D, their imaging technique could allow astronomers to study black holes smaller than M87’s, a monster with a mass of 6.5 billion suns, harbored in galaxies more distant than M87, which at 55 million light-years away, is still relatively close to our own Milky Way. The EHT is also laying the groundwork for extended observing campaigns to make movies of jet launching in M87.Now, a pair of Columbia researchers have devised a potentially easier way of gazing into the abyss. The EHT is pushing toward observing at 345 GHz (0.87 mm), which will enable imaging at even higher angular resolution. In addition to these two sources, the EHT observes a wide range of AGN sources with prominent jets, ranging from radio galaxies to blazars, at a resolution unobtainable with any other instrument. Sgr A* has no obvious jet and is orders of magnitude smaller than M87 in mass and accretion rate. M87 is a low-luminosity active galactic nucleus (AGN) source that launches a jet that is prominent at radio and optical wavelengths. The two main targets for general relativity, M87 and Sgr A*, are very different in astrophysical character. The EHT also aims to understand the astrophysics of supermassive black hole systems. M87 and Sgr A* are the primary targets in which the photon ring is easily resolvable by the EHT. Confirming that the inner edge of the ring is circular and of the predicted size constitutes a test of general relativity in a strong-field environment. General relativity predicts that a bright photon ring will appear whose size is proportional to the mass of the black hole. The EHT aims to image the region affected by strong gravitational lensing around supermassive black holes. The Sparse Modeling Imaging Library for Interferometry (SMILI) has proven to be better than traditional imaging methods at reconstructing super-resolved images. Haystack is at the forefront in algorithms to turn calibrated data into images. ![]() Haystack is in the middle of a development program to modernize HOPS based on lessons learned from years of handling EHT data. Originally designed in the 1990s to handle geodetic VLBI data, HOPS has proven to be well suited to the challenges of reducing millimeter VLBI data. ![]() The main EHT data reduction pathway uses the Haystack Observatory Post-processing System (HOPS). Event Horizon Telescope observations were made by observations around the globe data was sent to MIT Haystack Observatory and the Max-Planck-Institut für Radioastronomie for correlation Algorithms
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