These two globular star clusters, M15 and G1, harbor hundreds of thousands of stars. But deep within their dense cores is an unexpected guest: a class of intermediate-sized black holes. Black holes are invisible, but the probing eye of NASA's Hubble Space Telescope found them by measuring the velocities of stars whirling around the crowded cores. Using spectral observations, astronomers discovered that the stars orbiting the cores of M15 and G1 moved at a much faster rate, which suggested the presence of unseen massive bodies. These previously undiscovered black holes provide an important link that sheds light on the way in which black holes grow.
The new findings promise a better understanding of how galaxies and globular clusters first formed billions of years ago. Globular star clusters contain the oldest stars in the universe. If these clusters have black holes now, then they most likely had black holes when they formed billions of years ago.
The black hole in M15 [left] is 4,000 times more massive than our Sun. G1 [right], a much larger globular cluster, harbors a heftier black hole, about 20,000 times more massive than our Sun.
The globular star cluster M15 resides 32,000 light-years away in the constellation Pegasus. M15 is one of nearly 150 known globular clusters that form a vast halo surrounding our Milky Way galaxy. G1, located 2.2 million light-years away in the neighboring Andromeda galaxy (also known as M31), has a total mass of 10 million suns, making it one of the most massive globular clusters known.
The Hubble telescope photograph of M15 was taken December 1998 by the Wide Field and Planetary Camera 2. Hubble's Wide Field and Planetary Camera 2 also snapped the image of G1, in July 1994.
The members of the G1 research team are Michael Rich (University of California, Los Angeles/UCLA), Karl Gebhardt (University of Texas at Austin), and Luis Ho (Carnegie Institute of Washington). The members of the M15 research team are Roeland Van Der Marel and Joris Gerssen (Space Telescope Science Institute), Karl Gebhardt, Puragra Guhathakurta and Ruth Peterson (UCO/Lick Observatory, University of California at Santa Cruz), and Carlton Pryor (Rutgers University).
Credits
M15 image: NASA and The Hubble Heritage Team (STScI/AURA);G1 image: NASA and Michael Rich (UCLA);
Science: NASA, Roeland Van Der Marel and Joris Gerssen (Space Telescope Science Institute), Puragra Guhathakurta and Ruth Peterson (University of California Observatories/Lick Observatory), Carlton Pryor (Rutgers University), Michael Rich (UCLA), Karl Gebhardt (University of Texas), and Luis Ho (Carnegie Institution of Washington)
| About The Object | |
|---|---|
| Object Name | M15, NGC 7078 (right); G1 in M31, Mayall II (left) |
| Object Description | Globular Cluster in the Milky Way Galaxy |
| About The Data | |
| Data Description | M15 image: WFPC2 Data Principal Astronomers: H. E. Bond (STScI), D. R. Alves (Columbia Astrophysics Lab.), M. Livio, L. K. Fullton and K. G. Schaefer (STScI) STIS Data Principal Astronomers: R. Van Der Marel and J. Gerssen (STScI), K. Gebhardt (U. Texas at Austin), P. Guhathakurta and R. Peterson (UCO/Lick Observatory) and C. Pryor (Rutgers U.) G1 image: WFPC2 Data Principal Astronomers: M. Rich (UCLA), K. Mighell (NOAO), and J. Neill (Columbia U.), and W. Freedman (Carnegie Observatories) STIS Data Principal Astronomers: M. Rich (UCLA), K. Gebhardt (U. Texas at Austin), and L. Ho (Carnegie Inst. of Washington) |
| Instrument | HST>WFPC2 and HST>STIS |
| About The Object | |
|---|---|
| Object Name | A name or catalog number that astronomers use to identify an astronomical object. |
| Object Description | The type of astronomical object. |
| R.A. Position | Right ascension – analogous to longitude – is one component of an object's position. |
| Dec. Position | Declination – analogous to latitude – is one component of an object's position. |
| Constellation | One of 88 recognized regions of the celestial sphere in which the object appears. |
| Distance | The physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs. |
| Dimensions | The physical size of the object or the apparent angle it subtends on the sky. |
| About The Data | |
| Data Description |
|
| Instrument | The science instrument used to produce the data. |
| Exposure Dates | The date(s) that the telescope made its observations and the total exposure time. |
| Filters | The camera filters that were used in the science observations. |
| About The Image | |
| Image Credit | The primary individuals and institutions responsible for the content. |
| Publication Date | The date and time the release content became public. |
| Color Info | A brief description of the methods used to convert telescope data into the color image being presented. |
| Orientation | The rotation of the image on the sky with respect to the north pole of the celestial sphere. |
