Publications by authors named "F Eisenhauer"
Article Synopsis
- Brown dwarf companions to stars help us understand planet formation processes, but some of them are more massive than expected based on their luminosities and host star ages.
- Gliese 229 B, previously thought to be a single entity, was revealed through observations to actually be two brown dwarfs, Gliese 229 Ba and Bb, with masses of 38.1 and 34.4 Jupiter masses, respectively.
- This discovery challenges existing theories and raises questions about the formation and occurrence of binary brown dwarfs in close orbits around stars.
Tight relationships exist in the local Universe between the central stellar properties of galaxies and the mass of their supermassive black hole (SMBH). These suggest that galaxies and black holes co-evolve, with the main regulation mechanism being energetic feedback from accretion onto the black hole during its quasar phase. A crucial question is how the relationship between black holes and galaxies evolves with time; a key epoch to examine this relationship is at the peaks of star formation and black hole growth 8-12 billion years ago (redshifts 1-3).
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- The star S2, orbiting the black hole Sagittarius A*, undergoes notable changes in gravitational potential, which researchers use to test the local position invariance (LPI) part of the Einstein equivalence principle.
- By analyzing the redshift of hydrogen and helium absorption lines in the star's spectrum during its closest approach to the black hole, the study aims to establish an upper limit on LPI violations.
- The research findings suggest that the tested gravitational potential variation is six times greater than what can be measured on Earth and ten times larger than previous experiments with white dwarfs, marking a new testing regime for the LPI.
In general relativity, the angular radius of the shadow of a black hole is primarily determined by its mass-to-distance ratio and depends only weakly on its spin and inclination. If general relativity is violated, however, the shadow size may also depend strongly on parametric deviations from the Kerr metric. Based on a reconstructed image of Sagittarius A^{*} (Sgr A^{*}) from a simulated one-day observing run of a seven-station Event Horizon Telescope (EHT) array, we employ a Markov chain Monte Carlo algorithm to demonstrate that such an observation can measure the angular radius of the shadow of Sgr A^{*} with an uncertainty of ∼1.
View Article and Find Full Text PDFMeasurements of stellar orbits provide compelling evidence that the compact radio source Sagittarius A* at the Galactic Centre is a black hole four million times the mass of the Sun. With the exception of modest X-ray and infrared flares, Sgr A* is surprisingly faint, suggesting that the accretion rate and radiation efficiency near the event horizon are currently very low. Here we report the presence of a dense gas cloud approximately three times the mass of Earth that is falling into the accretion zone of Sgr A*.
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