an overabundance of x-ray binaries near the galactic center
DESCRIPTION
An Overabundance of X-ray Binaries Near the Galactic Center. Michael Muno (UCLA) with Fred Baganoff (MIT), Eric Pfahl (UVa), Mark Morris, Andrea Ghez, Jessica Lu (UCLA), Geoff Bower (Berkeley), Farhad Yusef-Zadeh, and Doug Roberts (Northestern). - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/1.jpg)
An Overabundance of X-ray Binaries Near the
Galactic Center
Michael Muno (UCLA)with
Fred Baganoff (MIT), Eric Pfahl (UVa), Mark Morris, Andrea Ghez, Jessica Lu
(UCLA), Geoff Bower (Berkeley), Farhad Yusef-Zadeh, and Doug Roberts
(Northestern)
![Page 2: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/2.jpg)
Five Years of Chandra Observations of the Galactic
Center• To search for rare objects, such as
accreting black holes and neutron stars.– How does accretion occur at low rates?
• To understand how the central 4 106 solar-mass black hole (Sgr A*) grows.– Why is Sgr A* accreting at such a low rate?– Does stellar dynamics feed stars into Sgr
A*?– How did dozens of young, massive stars
come to lie within 1 pc of Sgr A*?
![Page 3: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/3.jpg)
Five Years of Chandra Observations of the Galactic
Center
Sgr A*
5 pc
![Page 4: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/4.jpg)
X-rays from Accreting Compact Objects
•Most of the X-ray sources are accreting white dwarfs, the brightest 10% of which are detectable.• Accreting neutron stars and black holes are 100 times rarer, and most are accreting at low rates.
One Solar Radius
Image c
reate
s w
ith b
insi
m,
by R
ob H
yn
es
Location ofCompact Object
![Page 5: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/5.jpg)
Searching for Accreting Compact Objects
• Sources that produce sudden, bright outbursts are likely to be accreting black holes and neutron stars.
• We found 7 such transients within 25 pc of the Galactic center.
Sgr A*
5 pc
![Page 6: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/6.jpg)
Searching for Accreting Compact Objects
• Sources that produce sudden, bright outbursts are likely to be accreting black holes and neutron stars.
• We found 7 such transients within 25 pc of the Galactic center.
Sgr A*
New Transient
5 pc
![Page 7: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/7.jpg)
One Low-Mass X-ray Binary
The X-ray light curve displays partial eclipses at the 8 hour orbital period.
Infrared images reveal no infrared companion with K<15, ruling out a high-mass star.
Muno et al. (2005b)
![Page 8: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/8.jpg)
An Overabundance of X-ray Binaries in the Central Parsec
• 4 of 7 transients are within 1 pc of the Galactic Center.
• The chance of this happening randomly is less than 1 in 5000.
1 pc
Sgr A*
![Page 9: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/9.jpg)
Young High-Mass X-ray Binaries
• Seven Myr ago, several dozen massive stars formed from in a 104 Msun burst.
• Up to 300 black holes may have already descended from these stars.
• Up to 10% of these could be in HMXBs, or on order 30 systems.
Sgr A*
1 pc
Muno et al. (2005a)Infrared laser guide-star image courtesy W.M. Keck Observatory.
![Page 10: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/10.jpg)
• c = 7 106 Mo pc-3
• = 70 km s-1
Dynamically Forming LMXBs
1 pc
47 Tuc
• c = 6 104 Mo pc-3
• = 12 km s-1
Grindlay et al. 2001; Pooley et al. 2003
![Page 11: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/11.jpg)
LMXBs Form When Black Holes Capture Stars
• 104 black holes have dynamically settled into the central pc (Morris 1993, Miralda-Escudé &
Gould 2000).• Pfahl & Loeb (in prep.)
estimate that these form LMXBs via binary-single interactions at a rate of 10-6 yr -1.
• Over the dynamical time scale of 10 Gyr, 103 LMXBs could form.
simulation by E. Pfahl (Uva)
Muno et al. (2005)
![Page 12: An Overabundance of X-ray Binaries Near the Galactic Center](https://reader036.vdocuments.us/reader036/viewer/2022062322/568145ae550346895db2aa34/html5/thumbnails/12.jpg)
Summary• A faint radio and X-ray transient
provides the most direct evidence yet that accreting black holes release about half of their energy as jets.– This is also suspected to explain why Sgr A*
appears so faint in X-rays.
• Transient X-ray binaries are overabundant within 1 pc of Sgr A*.– This suggests that a cusp of compact
objects surrounds it, which would prevent low-mass stars from remaining in the region.