A pulsar close to our galaxy’s heart

Early in May, radio astronomers found something they’ve been longing for: a radio pulsar very close to the supermassive black hole (SBH) that marks the center of our Milky Way galaxy. Pulsars—rapidly spinning neutron stars—are precise celestial timers. At a distance of about half a light-year from the SBH, the new pulsar is not close enough to probe the strong distortion of spacetime expected within light-minutes. But it turns out to be close enough to yield the first direct measurement of the magnetic-field intensity B in the outskirts of the enveloping hot gas from which the SBH feeds. A team from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has used the institute’s 100-meter telescope (shown here) to make extensive measurements of the rotation of the polarization direction of the pulsar’s radio emission. That Faraday rotation depends sensitively on B in the pulsar’s immediate vicinity. They found that B is already quite strong (at least 8 milligauss) at the pulsar’s distance from the SBH. That’s an important, previously unknown parameter for the simulation of the black hole’s accretion dynamics. The team conjectures that the surprisingly large B at the outer limit of the accretion inflow might be responsible for the SBH’s puzzlingly anemic accretion rate, long known from the modest radio and x-ray emission coming directly from the galactic center. Having now found one radio pulsar in the galaxy’s innermost precinct, the team expects to find more. (R. P. Eatough et al., Nature, in press .)—Bertram Schwarzschild