Recent Results of the MPE Infrared/Submillimeter Group
ALMA Reveals the Rapid Evolutionary Lifecycle of Star-Forming Regions in Galaxies
Determining the physical processes controlling star formation in molecular clouds remains one of the main unsolved problems in astrophysics. New high-resolution observations of molecular clouds from ALMA and of the emission of young stars from the MPG/ESO 2.2 meter telescope for the nearby spiral galaxy NGC300 highlight the weak correlation of young stars and their parent clouds. This implies that the close correlation between molecular gas and star formation rate observed for whole galaxies and down to kpc scales – known as the Kennicutt-Schmidt or star formation relation – results from averaging over many star-forming relations. With a novel statistical model, we have shown that the observed decorrelation of young stars and molecular clouds holds valuable information on the time evolution of star-forming regions. For NGC300, we find that molecular clouds are short-lived (10 Myr or 1 dynamical timescale) and that a short period of active star formation (1.5 Myr) during which 2 to 3% of the cloud's mass is turned into stars releases sufficient stellar radiation and winds to disperse the parent molecular cloud. Star formation in molecular clouds proceeds very rapidly, yet highly inefficiently. This also explains the slow consumption of the galactic molecular gas reservoir by star formation of 1 Gyr in nearby galaxies because molecular gas has to evolve through many such cycles before it is fully turned into stars. We are now applying this analysis to a large number of galaxies in the nearby universe studied by the PHANGS collaboration and to first high-resolution observations of galaxies at high redshift during the peak of cosmic star formation.
- MPE press release
- Research paper: Kruijssen, Schruba et al., Nature Vol. 569, Issue 7757, p. 519–522
A Spatially Resolved Quasar Broad-Line Region
Knowing the structure, size, and dynamics of the broad-line regions (BLRs) near accreting supermassive black holes would allow scientists to constrain the inward and outward transport mechanisms and to infer the mass of the black hole. So far, however, directly measuring BLR properties was impossible because of the small physical size of the BLR, on the order of hundreds of light-days (corresponding to an angular size < 1 milliarcseconds). With GRAVITY, we have now, for the first time, spatially resolved (10 microarcseconds or ~ 0.03 parsec for a distance of 550 megaparsecs) a velocity gradient across the BLR of the quasar 3C 273. The gradient reveals rotation perpendicular to the jet, and is consistent with line emission from a thick disc of gravitationally bound material around a black hole of 3x108 M☉. We infer a disc radius of 150 light-days, compared to 100 to 400 light-days found previously with reverberation mapping (RM). Thus, GRAVITY provides both a confirmation of RM (at least for this one object) as the main previous method to determine black hole masses in quasars and a new and highly accurate, independent method to measure such masses. In an approved VLTI Large Program, we will extend this study to a (small) sample of local AGN, and we are exploring options to expand it to larger samples and higher redshifts with potential upgrades of GRAVITY.
More information: MPE press release
Measurement of Gravitational Redshift in the Galactic Center
Sagittarius A* (Sgr A*), the massive black hole in the center of our galaxy, is the closest of its kind and the largest in the sky. It is surrounded by a cluster of high-velocity stars, called the S-stars, whose trajectories are governed by the gravitational field of the black hole. We used the Very Large Telescope (VLT) instruments GRAVITY and SINFONI to follow the short (16-year) orbit star S2/S-02 during its recent pericenter passage in May 2018, and collected astrometric and spectroscopic data, respectively. For the first time, these joint data allowed for a robust detection of the combined gravitational redshift and transverse Doppler effect on S2/S-02.
Gravitational redshift is one of the three classic tests of general relativity. Einstein's theory foresees that due to gravitational time dilation, a light beam is stretched to longer wavelengths by a gravitational field. The change in the wavelength of light from S2/S-02 is inconsistent with Newtonian predictions and in excellent agreement with Einstein’s general theory of relativity. On a technological level, the success of this measurement with GRAVITY/VLT opens the door to an entirely new type of laboratory to probe and test the theory: the Galactic Center.
More information: GRAVITY Collaboration, 2018A&A...615L..15G