Space- VLBI mode

Millimetron space observatory as a part of a Space-Ground interferometer will allow to achieve extraordinary high angular resolution, which is needed to study very compact astrophysical objects– black holes, pulsars and masers.

The key science cases for this mode:

  • Black holes silhouettes

  • Radiatively-inefficient (weak) accretion flows

  • Jets physics

  • Binary systems with stellar mass black holes and micro-quasars

Space structure and physics near the black holes horizon, cosmic ray accelerators.

Black holes are the one of the most interesting predictions of General Relativity, and the attempts to prove or disprove their existence are the one of the main goals of astronomy. Black holes are extremely compact, so to observe the immediate vicinity of black holes it is required to have very high angular resolution. For all known objects, angular diameter of the black hole horizon is less than 20 mas. The progress in this area allows us to expect that the answer can be received in the near future. Thus, “Radioastron” ground- space interferometer best resolution is 7.5 mas and it is already conducting surveillance of a supermassive black hole in M87 galaxy. Ground "Event Horizon Telescope", working in the millimeter range may allow us to resolve the area of about the size of the black hole in the center of our Galaxy.

The model flux distribution on the black hole image in the M87 galaxy for different models of the emitting region. Source: V. Fish et al, High-Angular-Resolution and High-Sensitivity Science Enabled by Beamformed ALMA, arXiv astro-ph: 1309.3519

“Millimetron”, working in conjunction with ground-based telescopes will achieve the ultra-high angular resolution, which means that it could not only resolve the area of the size of a black hole, but also study in the details its surroundings: the gravitational lensing of the disk, the magnetic field structure. This will determine whether existing physical conditions can accelerate cosmic rays to ultrahigh energy, and deal with jet formation models.

Due to the high angular resolution it is intended to explore not only the two largest (in the angular size) black holes in our Galaxy and in M87, but at least 10 other sources covering a wide range of masses and accreting in different modes. Apart from supermassive black holes, it is planned to observe black holes of stellar masses in binary systems.

Rapid events: the structure and physics of powerfull explosions and their orientation, pulsars with flat spectra.

  • Determination of the asymmetry of supernova bursts

  • Search for afterglows of gamma -ray bursts and determination of their energy

  • Observation of the pulsar light cylinder

In the first days after the explosion of a supernova its remnant is extremely compact. However, the observation of this remnant in the early moments will help to measure the anisotropy and asymmetry of the original explosion, before the interaction with the environment will significantly distort the expansion trajectory of the supernova material.

Most pulsars have a spectrum which decreases rapidly with frequency. However, several objects showed flashes during which a pulsation at frequencies of tens of GHz was observed . Finding one such powerful enough flash will allow a ground-space interferometer to resolve the pulsar’s light cylinder and give invaluable information for the models of radiation of these objects.

The formation and evolution of galaxies, stars and planetary systems.

  • Structure of millimeter masers

Space masers are known to exist in the star forming regions in our and other galaxies, in stellar atmospheres, protoplanetary disks, supernovae remnants and even accretion disks around supermassive black holes. Due to maser amplification these objects have high enough brightness temperature and can be observed by the VLBI, but they are so compact that the most of maser spots are not resolved by the ground-based interferometers. Hence higher angular resolution is needed to study their physical parameters.

In the range of Millimetron the most well studied are water masers at the frequency of 22 GHz (wavelength 1.35 cm). The observations of such masers in the accretion disks of supermassive black holes in other galaxies (“megamasers”) allow to measure the black hole mass with the best precision and also to measure the cosmological distance with high precision.

Much less studied are the masers at higher frequencies. Water masers at 183.3 GHz, 232.7 GHz, 325.1 GHz and others, methanol (44GHz, 95GHz and others), SiO and other masers are known. The simultaneous observations of masers in the same object at different frequencies will help to improve our knowledge of the physical conditions of the maser amplification, and the high angular resolution is needed to study the spatial distribution of masers in the objects.