# How old is Sagittarius A\*? **URL:** \ **Category:** Factual Questions\ **Created:** [February 20, 2023, 8:19am UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072 "2023-02-20T08:19:08Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [February 20, 2023, 8:19am UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/1 "2023-02-20T08:19:08Z")
How old is it? What would be the process for a supermassive black hole to form? Is it because of its location at the Centre of the galaxy? (Question spawned by the discussion on destroying floppy disks.) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 20, 2023, 2:45pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/2 "2023-02-20T14:45:00Z")
It’s probably more the other way around: The black holes form first, and then become the nuclei of galaxies. We’ve never yet found a galaxy without a central black hole, so it’s probably as old as the galaxy itself. As to how it formed, though, that’s currently one of the big mysteries of astrophysics. The major competing models are the hierarchical model, where a large black hole is formed from the merger of a small number (2 or 3) smaller black holes, each of which was similarly formed by a merger of smaller black holes, until you get down to stellar sizes, or the accretion model, where you start off with one small black hole that just continually accretes material until it’s a large black hole. Neither one, though, seems to be consistent with all the observations. ---
**Author:** ![Polarity](https://avatars.discourse-cdn.com/v4/letter/p/7cd45c/32.png) [@Polarity](https://boards.straightdope.com/u/Polarity)\ **Post date:** [February 20, 2023, 3:20pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/3 "2023-02-20T15:20:00Z")
I think there is also the direct collapse theory. Where a massive gas cloud directly collapses into a supermassive black hole, but some condition prevents it from ever becoming a star in the first place. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [February 20, 2023, 3:21pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/4 "2023-02-20T15:21:24Z")
This may be of interest: > **[The Center of the Milky Way May Be Chock-Full of Black Holes](https://www.smithsonianmag.com/smart-news/center-milky-way-may-be-chock-full-black-holes-180968697/)** > > Researchers spotted about a dozen black holes lurking at our galactic center—and there may be up to 10,000 more ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [February 20, 2023, 3:40pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/5 "2023-02-20T15:40:59Z")
I should have added that, while the original black hole at the center may be as old as the galaxy itself it is likely it has grown over time as younger black holes merge with it. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 20, 2023, 3:53pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/6 "2023-02-20T15:53:20Z")
It’s nearly a tautology that it’s grown over time. The question is just how much it’s grown over time, and whether the rate of growth is steady or sporadic. The right answer will probably turn out to be some mix of the prevailing models, but right now, we don’t know what the mix is. And dark matter is likely to be relevant, as well, which just adds more that we don’t know. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [February 20, 2023, 5:21pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/7 "2023-02-20T17:21:17Z")
[Pretty old](https://www.space.com/primordial-black-holes-explain-dark-matter-universe-mysteries). ---
**Author:** ![Quintas](https://avatars.discourse-cdn.com/v4/letter/q/48db29/32.png) [@Quintas](https://boards.straightdope.com/u/Quintas)\ **Post date:** [February 20, 2023, 5:29pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/8 "2023-02-20T17:29:48Z")
Below is an interesting short vid on ‘Black Hole stars’. I don’t know if the idea is considered fringe or not. The gist of it being that currently there is an upper size limit to stars. After a certain size, their solar wind blows away any remaining dust or gas before it can be added to the stars mass. However, in the much denser early universe, stars of phenomenal size may have formed. Individual stars the size of our entire solar system, and therefore the origin of supermassive black holes and eventually galaxies. [![](https://img.youtube.com/vi/aeWyp2vXxqA/maxresdefault.jpg "Black Hole Star – The Star That Shouldn't Exist") ](https://www.youtube.com/watch?v=aeWyp2vXxqA) ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [February 20, 2023, 5:31pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/9 "2023-02-20T17:31:12Z")
Thank you. Very helpful. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [February 20, 2023, 5:52pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/10 "2023-02-20T17:52:02Z")
If such monsters ever existed why do we not see any? You’d think they’d stand out. ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [February 20, 2023, 6:52pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/11 "2023-02-20T18:52:14Z")
> [@Chronos](#): > > As to how it formed, though, that’s currently one of the big mysteries of astrophysics. The major competing models are the hierarchical model, where a large black hole is formed from the merger of a small number (2 or 3) smaller black holes, each of which was similarly formed by a merger of smaller black holes, until you get down to stellar sizes, or the accretion model, where you start off with one small black hole that just continually accretes material until it’s a large black hole. Neither one, though, seems to be consistent with all the observations. Do they necessarily need to be at a galaxy center? Are there smaller, free roaming ones out there, like say, Oumuamua. ---
**Author:** ![Quintas](https://avatars.discourse-cdn.com/v4/letter/q/48db29/32.png) [@Quintas](https://boards.straightdope.com/u/Quintas)\ **Post date:** [February 20, 2023, 6:59pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/12 "2023-02-20T18:59:25Z")
> [@Whack-a-Mole](#): > > If such monsters ever existed why do we not see any? You’d think they’d stand out. In Wikipedia they are referred to a ‘Quasi-Stars’ > **[Quasi-star](https://en.wikipedia.org/wiki/Quasi-star)** > > A quasi-star (also called black hole star) is a hypothetical type of extremely massive and luminous star that may have existed early in the history of the Universe. Unlike modern stars, which are powered by nuclear fusion in their cores, a quasi-star's energy would come from material falling into a black hole at its core. > A quasi-star would have resulted from the core of a large protostar collapsing into a black hole, where the outer layers of the protostar are massive enough to absorb the res... The article does not answer your question but could it possibly be the Universe was still opaque that early in it’s history? The article also states they would have had a very short lifespan of around 7 million years. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [February 20, 2023, 7:13pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/13 "2023-02-20T19:13:43Z")
Do we have an idea about what fraction of a black hole’s mass is from dark matter vs charged matter? (I know it doesn’t matter now what type of matter it was; I’m asking about stellar evolution.) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 20, 2023, 7:27pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/14 "2023-02-20T19:27:09Z")
We can make guesses, but there’s no consensus on the guesses, and currently no way to tell which guesses are correct. And those super-sized quasi-stars, if they ever existed, don’t exist any more, because they’ve become black holes. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [February 20, 2023, 7:34pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/15 "2023-02-20T19:34:46Z")
> [@Chronos](#): > > And those super-sized quasi-stars, if they ever existed, don’t exist any more, because they’ve become black holes. But, telescopes like the James Webb can see back in time [13.5 billion years](https://webb.nasa.gov/content/science/firstLight.html). That’s pretty close to when it all got started after the universe stopped being opaque. So, if one existed, it seems reasonable to think Webb could see one. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 20, 2023, 7:42pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/16 "2023-02-20T19:42:59Z")
What we see when we look back that far is entire galaxies. One of those quasi-stars would be a heck of a lot brighter than a modern star, but it’d still be far, far dimmer than an entire galaxy. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [February 20, 2023, 8:00pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/17 "2023-02-20T20:00:54Z")
> [@Whack-a-Mole](#): > > Webb could see one > [@Chronos](#): > > What we see when we look back that far is entire galaxies And with current telescopes we may already be close to the theoretical resolution limit for such old objects, caused by cumulative quantum effects over very large distances. > **[The universe's resolution limit—why we may never have a perfect view of...](https://phys.org/news/2015-11-universe-resolution-limitwhy-view-distant.html)** > > Can you make out the dot at the bottom of this question mark? What if you stand a few metres away? The finest detail the average human eye can distinguish is about the size of a full stop seen at a distance of a metre. This is called "resolution".... This was a theoretical paper from 2015, I don’t know if we yet have any data from James Webb that provides evidence to support or refute it. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [February 20, 2023, 8:17pm UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/18 "2023-02-20T20:17:50Z")
So…do we think that these super-sized quasi-stars were only an occasional quirk in the early galaxies or were whole galaxies composed of them and then they blew up and reformed into more usual stars or were they pre-galaxies? Just gigantor stars kinda floating around on their own? (Or something else?) It seems like the early universe was much more dense so forming such monster stars would be much more likely. (Just guessing though) ---
**Author:** ![Quintas](https://avatars.discourse-cdn.com/v4/letter/q/48db29/32.png) [@Quintas](https://boards.straightdope.com/u/Quintas)\ **Post date:** [February 21, 2023, 4:29am UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/19 "2023-02-21T04:29:56Z")
> [@Whack-a-Mole](#): > > Just gigantor stars kinda floating around on their own? (Or something else?) > > It seems like the early universe was much more dense so forming such monster stars would be much more likely. (Just guessing though) That was my take on it. Just gigantor stars floating on their own. The resulting super massive black holes becoming the ‘seeds’ of later galaxy formation. I think i’ll submit the question to the StarTalk podcast. (Neil DeGrasse Tyson’s weekly podcast). I’m a patreon and it looks like I can submit one question for consideration per month, although no guarantee he’ll feature it. ---
**Author:** ![Ponderoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ponderoid/32/19221_2.png) [@Ponderoid](https://boards.straightdope.com/u/Ponderoid)\ **Post date:** [February 21, 2023, 4:49am UTC](https://boards.straightdope.com/t/how-old-is-sagittarius-a/980072/20 "2023-02-21T04:49:28Z")
Ask him to bring on [Dr Becky](https://www.youtube.com/channel/UCYNbYGl89UUowy8oXkipC-Q) to help him answer it.