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Surfing a Black Hole

Star Orbiting Massive Milky Way Centre Approaches to within 17 Light-Hours

Wednesday, October 16, 2002
The European Southern Observatory

PR Photo 23a/02 is a reproduction of an image of the innermost area of the Milky Way, only a few light-years across, obtained in mid-2002 with the NACO instrument at the 8.2-m VLT YEPUN telescope. It combines frames in three infrared wavebands between 1.6 and 3.5 µm. The compact objects are stars and their colours indicate their temperature (blue = "hot", red = "cool"). There is also diffuse infrared emission from interstellar dust between the stars. The two yellow arrows mark the position of the black hole candidate "SgrA*" at the very centre of the Milky Way galaxy. The scale is indicated; the 1 light-year bar subtends an angle of 8 arcsec in the sky.
[full size image]
Image Credit: ESO.

ESO Press Release 17/02
Summary
An international team of astronomers, lead by researchers at the Max-Planck Institute for Extraterrestrial Physics (MPE), has directly observed an otherwise normal star orbiting the supermassive black hole at the center of the Milky Way Galaxy.

Ten years of painstaking measurements have been crowned by a series of unique images obtained by the Adaptive Optics (AO) NAOS-CONICA (NACO) instrument on the 8.2-m VLT YEPUN telescope at the ESO Paranal Observatory. It turns out that earlier this year the star approached the central Black Hole to within 17 light-hours -- only three times the distance between the Sun and planet Pluto -- while travelling at no less than 5000 km/sec.

"SgrA*" and S2 are identified in the left panel. The right panel displays the orbit of S2 as observed between 1992 and 2002, relative to SgrA* (marked with a circle). The positions of S2 at the different epochs are indicated by crosses with the dates (expressed in fractions of the year) shown at each point. The size of the crosses indicates the measurement errors. The solid curve is the best-fitting elliptical orbit - one of the foci is at the position of SgrA*. The 2002 data points come from NACO observations done during the early commissioning, fine adjustement, and Science Verification phases for this instrument; these data were promptly made public through the ESO Archive, cf. the NACO data webpage.
[full size image]
Image Credit: ESO.

Previous measurements of the velocities of stars near the center of the Milky Way and variable X-ray emission from this area have provided the strongest evidence so far of the existence of a central Black Hole in our home galaxy and, implicitly, that the dark mass concentrations seen in many nuclei of other galaxies probably are also supermassive black holes. However, it has not yet been possible to exclude several alternative configurations.

In a break-through paper appearing in the research journal Nature on October 17th, 2002, the present team reports their exciting results, including high-resolution images that allow tracing two-thirds of the orbit of a star designated "S2". It is currently the closest observable star to the compact radio source and massive black hole candidate "SgrA*" ("Sagittarius A") at the very center of the Milky Way. The orbital period is just over 15 years.

The photo shows an infrared NACO image of a ~ 2 x 2 arcsec2 area, centred on the position of the compact radio source "SgrA*" at the centre of the Milky Way Galaxy; it is marked by a small cross. The image was obtained in the Ks-band at wavelength 2.1 µm in May 2002 and the angular resolution (image sharpness) is about 0.060 arcsec. At about the same time, the star designated "S2" came within 0.015 arcsec of the radio source. At the distance of the Milky Way Center, 1 arcsec on the sky corresponds to 46 light-days; the bar is 20 light-days long (0.44 arcsec).
[full size image]
Image Credit: ESO.

The new measurements exclude with high confidence that the central dark mass consists of a cluster of unusual stars or elementary particles, and leave little doubt of the presence of a supermassive black hole at the centre of the galaxy in which we live.
(More: ESO.org News Source)
2002 © European Southern Observatory.

Dan