Black Hole in 47 Tuc

[glend]

In an article today concerning the discovery of "Middle-weight Black Holes" it is mentioned that 47 Tuc is the home of this black hole.

"The discovery was announced today in the journal Nature, revealing the black hole hid at the centre of the 12-billion-year-old globular 47 Tucanae star cluster."

http://www.abc.net.au/news/2017-02-09/middleweight-black-hole-found-in-space-qld-scientist-says/8253468

I must admit I had never associated black holes with clusters, thinking of them more as galaxy engines.:eyepop:

[Atmos]

I wrote a "paper" (never published) a couple of years ago that looked at low metallicity globular clusters as likely candidates for the creation of intermediate mass black holes.
There isn't a lot of research on this yet as discovering them is VERY difficult. In part because they're so damned difficult to find at the best of times but also because they tend to form towards the cores of globular clusters where it is even more difficult to resolve.

[geolindon]

very cool on a few levels :)

a neat advance in knowledge and understanding

an Aussie (Qldr) did the modeling

lends more significance to one of the best AA sights

AND congrats Colin for being on the money!!:thumbsup:

L

[ChrisV]

Can I ask. Why didn't it get published ? I work in a biological (not a physical) science and would never pass an opportunity to publish.

[Atmos]

I referenced some far more in depth papers, what I did looked at the evolution of globular clusters of different metallicities and it was just a discussion point for me.

Getting it published is a bit of a nightmare especially when you're not working for a university or institution at the time. Costs a fair amount, takes many months and umpteen revisions until they're happy with it. Was more effort than it would be worth. Apart from pointing to a hole in the AGB evolution used in one of the Swinburne stellar simulators, it didn't really add anything new as such. Collated information, could get it published as a Letter or something I suppose :)

[astroron]

Reading that link,one thing that caused me to think was, why would there be such a large black hole in a globular cluster:question:
I know GC's are old and all that stuff, but what would drive a black hole if there is no gas etc, and there hasn't been any for at least 12 billion years.
Just asking as it seems counter intuitive to me.
Cheers:thumbsup:

[Atmos]

Just read it :) I'll do a dot point progression.

- Stars formed earlier in the universes history has less metals (elements other than hydrogen and helium).
- Molecular Clouds with a lower metallicity will form statistically larger stars than the present day. They burn faster and hotter so a more "efficient" at making black holes.
- Globular Clusters are gravitationally bound so many of what originally formed is still there (except gas).
- Stars larger than maybe 15-18 solar masses formed black holes.
- Gravitational interactions in a closed system tend to force heavier objects towards their cores (black holes move towards the centre).
- Stellar mass black holes merge and become intermediate mass black holes.

[sjastro]

Very interesting Colin.

How does one actually detect black holes in globular clusters, the Keplerian orbits of nearby stars?

Another possibility of detection is during the black hole merger.
Now that we know gravitational waves are the real deal and there will a number of gravitational wave detectors coming on line in the next few years, the incidence of black hole mergers will increase and most importantly the ability of pinpointing the source.

Regards

Steven

[glend]

Detection methodology is explained in the original post. It looks at the gravitational effects the middle-weight black hole has on stars in the cluster.

[sjastro]

Thanks for that.
Unfortunately pop sci articles are not terribly descriptive.

The Nature article explains it far better.
http://www.nature.com/articles/nature21361.epdf?referrer_access_to ken=Pv9xPzxfIwXTVJJZE3xnMtRgN0jAjWe l9jnR3ZoTv0N5AmBcFNjw6sn5C8wVWQI-Vuc-NWjQEcRH4ddMgHOZGAB7TGkUvc7r3Pol0Q-lMU4qHplrWhVWogHWUtMX3jIRT9xJ3of6mp 82GadkkXIw8ovgjNfhtw2_PPG9GbubN8-8RGsCrVsjsN9IpImAW8HiI4TziQHxz0Kcf2 T36MtOLqYy_GRO1MZR2OIP9QnUy3RPHOG8-MXQH6fOQMdJ9AVg8h8g4Tt-fforBrKUd9sGoJ44phEnuYm6i42JI5ow4MY %3D&tracking_referrer=www.smithsonianma g.com

[glend]

Well excuse me for posting it. I will leave it to you.

[ChrisV]

The nature paper was pretty heavy going. Pop culture dont seem too bad.

[sjastro]

Chris,

Unfortunately the "pop culture" article left more questions than answers.

The Nature paper assumes a basic knowledge of Stellar Dynamics.
In gravitational bound stellar systems such as open and globular clusters, stars interact with each other and exchange momentum and kinetic energy.

The more massive the star the less the velocity hence massive stars tend to be in lower orbits and occupy the centre of the cluster.
This is the mass segregation term mentioned in the article.
Since stars exchange kinetic energy there is a statistical tendency for the kinetic energy to equalize amongst stars.
This is the energy equipartition description in the article.
The time taken for equalization to occur is the relaxation time.

Since kinetic energy is equalized, the lower mass stars receive a larger velocity boost and can exceed the escape velocity of the cluster.
These are the familiar "star streamers" found in globular cluster images.
Other stars are pushed out into higher orbits.

The presence of a black hole at the centre changes the mass segregation and alters the velocity distribution of stars versus distance from the centre of the cluster.

The data is gathered from pulsars in the cluster.
Pulsars closer to the centre of cluster have their rotations slowed down by gravity which can measured as a Doppler shift.

From this the velocity distribution versus the distance from the centre can be determined.

Regards

Steven

[batema]

This is so interesting. Thanks everyone for your expertise.

Mark.

[Pinwheel]

Interesting, I visualized it as a drain whirlpool in reverse. Excuse my interpretation if I have the image wrong.