Heaviest Stellar Black Hole in Nearby Galaxy CXC release

Oct. 17, 2007

A 15.65 M in an eclipsing binary in the nearby spiralGalaxy Messier 33 ……Nature 449, 972-875 (18 Oct. 2007)

(Orosz)J. A. Orz, J. E. McClintock, R. N.arayan, C. D. Bailyn, J. D. Hartman, L. Marci, J. Liu, W. Pietsch, R. A. Remillard, A. Shopper & T. Mazeh (Shporer)

Chandra X-ray & Hubble Optical Images of M33 X-7

The composite image includes data from NASA's Chandra X-ray Observatory (blue) and the Hubble Space Telescope. The bright objects in the inset image are young, massive stars around M33 X-7, and the bright, blue Chandra sourceis M33 X-7 itself. X-rays from Chandra reveals how long the black hole is eclipsed by the companion star, which indicates the size of the companion.

M33 X-7 with Scale Bar

Chandra X-ray Image of M33 X-7

These two Chandra images show M33 X-7 when the black hole in this binary is not being eclipsed (upper) and when it is being eclipsed (bottom). M33 X-7 is located in the center of the image.

Kitt Peak Optical Image of M33Located in the constellation of Triangulum, M33 is a nearby face-on spiral galaxy. It is over thirty thousand light years across. M33, our galaxy and the Andromeda Galaxy (a.k.a. M31) are the three major galaxies of our corner of the Universe, a small group of galaxies known as "The Local Group."

Gemini Optical Image of M33 X-7Astronomers have located an exceptionally massive black hole - almost 16 times the mass of the Sun - in orbit around a huge companion star. By combining observations from NASA's Chandra X-ray Observatory with optical data from the Gemini telescope, the black hole known as M33 X-7 was determined to be the most massive black hole in its class.

Almost the mass of all the stellar black holes are 10 M. Although some of them areheavier (ex: V1487 Aql & V404 Cyg), the estimation of their masses are quite imprecise.

Masses of Stellar Black Hole

Mean optical spectrum of M33 X-7

Phased X-ray light curve and radial velocity curve for M33 X-7

Scenario of the evolution in M33 X-7A ~16 M black hole paired with a ~70 M secondary with a separation of only ~42 R system

˝Common envelope˝ phase results in a significant amount of mass lost from the parent star, and very little mass gained by the secondary. --- The outer envelope of the progenitor needs to be intact until core He burning completed.1. The mass donor needs to be at least 1.2 times more massive than the secondary.2. The radius of the mass donor at the end of core He burning needs to be larger than its radius at the end of core H burning.

The present-day mass loss rate: 2.6X10-6 Myr-1---the secondary star has lost 5.2-7.8 M.

Initial mass of the secondary near 80 M. For a common envelope phase to occur, the progenitor star

should more massive than 96 M. Problematic!!

According to evolutionary models---an extreme case of initial mass of 120 M

the mass after H burning is ~52.9 M and after He burning is ~17.2 M

Owing to the large amount of mass loss, the radius of the star after core He burning is smaller than

the radius after core H burning. Conflict!!

So the progenitor star of M33 X-7 lost roughly an order of magnitude less mass before the commonenvelope phase ensued than is predicted by evolutionary models.

Summary1. M33 X-7 is the first black hole in a binary system observed to undergo eclipses.

The eclipse nature enables unusually accurate estimates for the mass of the black hole and its companion.

2. This is a huge star that is partnered with a huge black hole. Eventually, the companion will also go supernova and then we’ll have a pair of black holes.

3. This discovery raises all sorts of questions about how such a big black hole could have been formed. If even more massive stars all lose very little material, it could explain the incredibly luminous supernova seen as SN 2006gy. (The parent star of SN 2006gy is thought to be 150 M when it exploded) The determination of an accurate mass for M33 X-7 -- located at a distance of more than 16 times that of any other confirmed stellar black hole -- marks a major advance in our capability to study black holes in Local Group galaxies beyond the Milky Way.