APOD: At the Heart of Orion (2015 Jan 02)

[APOD Robot]

At the Heart of Orion

Explanation: Near the center of this sharp cosmic portrait, at the heart of the Orion Nebula, are four hot, massive stars known as the Trapezium. Tightly gathered within a region about 1.5 light-years in radius, they dominate the core of the dense Orion Nebula Star Cluster. Ultraviolet ionizing radiation from the Trapezium stars, mostly from the brightest star Theta-1 Orionis C powers the complex star forming region's entire visible glow. About three million years old, the Orion Nebula Cluster was even more compact in its younger years and a dynamical study indicates that runaway stellar collisions at an earlier age may have formed a black hole with more than 100 times the mass of the Sun. The presence of a black hole within the cluster could explain the observed high velocities of the Trapezium stars. The Orion Nebula's distance of some 1,500 light-years would make it the closest known black hole to planet Earth.

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[hoohaw]

We are lucky that a segment of the Galaxy is tipped out of the Galactic plane, giving us a clearer view of this active star formation region: there is little foreground addition to the scene. Convenient!

[BDanielMayfield]

About three million years old, the Orion Nebula Cluster was even more compact in its younger years and a dynamical study indicates that runaway stellar collisions at an earlier age may have formed a black hole with more than 100 times the mass of the Sun.

I enjoyed reading the dynamical study link and the conclusions in the referenced paper. I also remember well reading and commenting about the news of this study when it was reported in the linked to Sky and Telescope news blog.

Bruce

[Nitpicker]

We are lucky that a segment of the Galaxy is tipped out of the Galactic plane, giving us a clearer view of this active star formation region: there is little foreground addition to the scene. Convenient!

The (back side of the) galactic equator passes through the constellation Orion (near his right arm and club), so M42 is slightly further out from the galactic centre than we are.

[starsurfer]

I think there is a star in the constellation of Columba to the south of Orion that was ejected from the Orion Nebula Cluster.

[Ann]

I think there is a star in the constellation of Columba to the south of Orion that was ejected from the Orion Nebula Cluster.

Oh yes! It's Mu Columba(e), one of my favorite stars! It is very blue!

Ann

[DavidLeodis]

I am having trouble definitely spotting the Trapezium in the image. The explanation states it comprises 4 stars, so I assume it is the grouping just above and right of centre (UK English spelling ) that has 3 stars about in a line and the bright 1 just above them, but it takes me some convincing that it looks like a trapezium. There does however seem to me to be a more trapezium-like shape if the line of 3 stars are used and then a bright star above and left of them and a bright star above and a bit further to their right, but that shape has 5 stars so cannot be the Trapezium. I'm .

[BDanielMayfield]

I think there is a star in the constellation of Columba to the south of Orion that was ejected from the Orion Nebula Cluster.

Oh yes! It's Mu Columba(e), one of my favorite stars! It is very blue!

Ann

Well done starsurfer, and great links Ann. From your first I quote from Jim Kaler's description:

Mu Columbae and its partner AE Aurigae are the classic "runaway stars." Mu is moving at high speed -- 117 km/s -- relative to the Sun, and is moving directly away from AE Aur at over 200 km/s. The two must once have been together, and are now separated by some 70 degrees. Modern computers allow the tracks of the two to be traced back in time, and show that the pair crossed paths near Orion's current Trapezium (Theta-1 Ori) sometime around 2.5 million years ago. The third actor in the drama seems to be Iota Orionis (Na'ir al Saif), a multiple star whose main component is a very close double with an unusually highly eccentric orbit. It seems that 2.5 million years ago -- before the Trapezium (only a million or so years old) itself was even born -- two double stars crashed into each other, swapped two members and ejected two others at high velocity, thus connecting Columba, Orion, and Auriga. More oddly perhaps, runaways are not all that unusual, as they constitute 10 to 15 percent of all O and B stars. There seem to be two routes to runaway glory, double star encounters as presented here, and supernova explosions in doubles in which the exploder pops off off-center, going off in one direction while ejecting its companion in the other, a classic case being Zeta Ophiuchi. Such will most likely be the fate of Mu. The so-called "fixed stars" are hardly so!

No mention there of the possible role of a >100 solar massed black hole in the heart of Orion as discussed in this apod's description, but that's very understandable since the Subr et al paper is more recent. I wonder how much traction their black hole in the ONC theory has garnered in the professional astronomical community? Some at least, since their work has now been referenced here.

Bruce

[rstevenson]

I am having trouble definitely spotting the Trapezium in the image. The explanation states it comprises 4 stars, so I assume it is the grouping just above and right of centre (UK English spelling ) that has 3 stars about in a line and the bright 1 just above them, but it takes me some convincing that it looks like a trapezium. There does however seem to me to be a more trapezium-like shape if the line of 3 stars are used and then a bright star above and left of them and a bright star above and a bit further to their right, but that shape has 5 stars so cannot be the Trapezium. I'm .

Actually, there are quite a few stars in the Trapezium area, with 5 being quite bright. But 2 of the 5 are close together, hence its common name. I think this little diagram I just made from a crop of the large image shows the Trapezium...

Trapezium.jpg

And here's a NASA/Hubble image with the 5 stars labelled...

TrapeziumStars.jpg

Rob

[Ann]

BruceDanielMayfield wrote:

No mention there of the possible role of a >100 solar massed black hole in the heart of Orion as discussed in this apod's description, but that's very understandable since the Subr et al paper is more recent. I wonder how much traction their black hole in the ONC theory has garnered in the professional astronomical community? Some at least, since there work has now been referenced here.

As some of you might remember, I was quite incredulous when I heard about the supposed black hole in the Orion Nebula, and I protested quite loudly. I was told by those who understand these things better than I do that I can't jump to conclusions when I have no knowledge or deeper understanding of the thing I'm talking about, which is something I have to acknowledge.

But I made a quick googling to try to find out how interested the scientific community has been in the idea of a black hole in the Orion Nebula since the possibility of its existence was first proposed, and my impression is that the answer is, not very. I googled "orion nebula black hole" and got 221,000 results. Not bad. But on the first Google page, all the results except two were from September, October or November 2012. One of these "not from 2012 results" was a page that seems more like popular science than "hard science" to me, and the other one was a Wikipedia article (or stub) which said:

A 2012 paper suggests an intermediate mass black hole with a mass >100 times larger than that of the Sun may be present within the Trapezium, something that could explain the large velocity dispersion of the stars of the cluster.[5]

5. Ladislav Subr, Pavel Kroupa, Holger Baumgardt. "Catch me if you can: is there a runaway-mass black hole in the Orion Nebula Cluster?". Retrieved 2012-10-06

To me this suggests that there haven't been any other papers that have looked into the possibility of a black hole in the Orion Nebula since the idea was proposed in 2012.

Ann

[BDanielMayfield]

Well then I'm favorably impressed that this black hole in the ONC possibility, which seems to be slightly out of bounds consensus-wise, was favored with a mention here. I think that if Subr et al's ideas are right it would help to explain the present day SN occurrence rate. A few more black holes and several times less O and B stars helps the pressent day universe to be more habitable.

Bruce

[DavidLeodis]

Thanks Rob for your very helpful response to my query about where the Trapezium is in the image.

[geckzilla]

How would you study black holes in the Orion Nebula, Ann? It sounds about as easy as studying the possibility that a large dinosaur once stood in the very spot your house currently occupies. You can guess at some vague probability that it happened at one point but unless there just happens to be fossil evidence then your efforts will be fruitless. It's the same way with black holes. Unless they are active or being orbited by a visible object, there is no way of knowing where one is. But if there is evidence that massive stars previously existed in a position that have long since exploded and left shock fronts and impressions on nearby gas and dust then you can guess that maybe there is a black hole tucked away invisibly.

If you had the largest telescope imaginable and pointed it right at an inactive black hole for a very long time, I suppose you could acquire something like a Hubble eXtreme Deep Field and then if some galaxy just happened to line up with the black hole you could observe a distortion. I have to wonder how small the chance of having a galaxy or a piece of a galaxy just happen to line up behind the black hole would be. Ugh, it makes my head hurt.

[BDanielMayfield]

Since it will be well neigh impossible to actually see direct evidence of an ONC BH for the foreseeable future, astronomers will have to rely on indirect dynamical studies to rule this possibility either in or out. The forthcoming Gaia data on stellar motions might go a long way toward settling this.

Bruce

[Chris Peterson]

Since it will be well neigh impossible to actually see direct evidence of an ONC BH for the foreseeable future, astronomers will have to rely on indirect dynamical studies to rule this possibility either in or out. The forthcoming Gaia data on stellar motions might go a long way toward settling this.

I am curious about this distinction you draw between "direct" and "indirect" evidence. We are currently capable of detecting a 100 M_sun black hole by observing how it gravitationally perturbs nearby stars (or a hypothesized companion), or by observing EM outbursts when it is in an accretionary phase (possible due to the dust and gas rich environment of the nebula). Either would represent very strong evidence, regardless of whether you categorized it as "direct" or "indirect".

[BDanielMayfield]

How would you study black holes in the Orion Nebula, Ann? It sounds about as easy as studying the possibility that a large dinosaur once stood in the very spot your house currently occupies.

Finding a fosilized Dino footprint under Ann's house should actually be quite doable, if any happened to be there. Drill baby, drill for the right rock formation, employ ground penetrating radar and then dig as deep as needed. Sorry about what that would do to to your house Ann.

Bruce

[geckzilla]

Fossils are not really that easy to find. Chances of losing remains to entropy through various forces are pretty high. There is a pretty good chance there are no large fossils of any sort below Ann's house. Perhaps I should have created a better metaphor...

[BDanielMayfield]

Fossils are not really that easy to find. Chances of losing remains to entropy through various forces are pretty high. There is a pretty good chance there are no large fossils of any sort below Ann's house. Perhaps I should have created a better metaphor...

I completely agree that fossils are rare at any random point on Earth, and that entropy, etc. destroy most fossil evidence over time. My only point was that the rocks under Ann's house are much more accessible than the heart of the Orion Nebular Cloud.

[geckzilla]

Fossils are not really that easy to find. Chances of losing remains to entropy through various forces are pretty high. There is a pretty good chance there are no large fossils of any sort below Ann's house. Perhaps I should have created a better metaphor...

I completely agree that fossils are rare at any random point on Earth, and that entropy, etc. destroy most fossil evidence over time. My only point was that the rocks under Ann's house are much more accessible than the heart of the Orion Nebular Cloud.

I don't know about that. I've seen hundreds of pictures of Orion but I have definitely never seen the rocks under Ann's house.

[BDanielMayfield]

Since it will be well neigh impossible to actually see direct evidence of an ONC BH for the foreseeable future, astronomers will have to rely on indirect dynamical studies to rule this possibility either in or out. The forthcoming Gaia data on stellar motions might go a long way toward settling this.

I am curious about this distinction you draw between "direct" and "indirect" evidence. We are currently capable of detecting a 100 M_sun black hole by observing how it gravitationally perturbs nearby stars (or a hypothesized companion), or by observing EM outbursts when it is in an accretionary phase (possible due to the dust and gas rich environment of the nebula). Either would represent very strong evidence, regardless of whether you categorized it as "direct" or "indirect".

I defer to your superior knowledge on this Chris, but my thinking was informed by a response that Dr. Monica Young gave to myself and others in the comments to the S&T news story she wrote back in 2012 on their website. Readers like myself had asked, 'if there was a >100M_SUN black hole in the ONC, wouldn't it have produced detectable evidence?' Her response was:

There are some great questions here, and hopefully the following will answer a few of the outstanding questions: If there is a black hole in the Orion Nebula Cluster, it’s unlikely that it’s accreting much gas. So it won’t emit many X-rays from its accretion disk, and it won’t form jets strong enough for us to see. That’s why the main test for its existence is the motion of stars in the very inner core of the cluster, which requires a higher degree of resolution than what’s been done in the past.

So to answer your question Chris to me "direct evidence" would be signs of accretion disk and/or jet effects and/or the motions of inner core stars that Dr. Young mentioned, whereas "indirect evidence" could be stellar motions of a much broader category like the runaway stars that were described in the above Jim Kaler quote, as well as the absence of the expected numbers of OB stars that Subr's BH theory attempts to explain.

Bruce

[Ann]

Geck wrote:
How would you study black holes in the Orion Nebula, Ann?

I wouldn't.

I just thought... either the idea that there is a black hole in the Orion Nebula has been accepted by the astronomical community, or else someone else might want to look at the calculations and assumptions behind the hypothesis that there is, and see if they can come up with an alternative hypothesis. After all, the idea that there is a black hole in the Orion Nebula rests on the observation that the stars in the Trapezium region are moving very fast:

http://en.wikipedia.org/wiki/Trapezium_Cluster wrote:

A 2012 paper suggests an intermediate mass black hole with a mass >100 times larger than that of the Sun may be present within the Trapezium, something that could explain the large velocity dispersion of the stars of the cluster.

And as Chris said,

We are currently capable of detecting a 100 Msun black hole by observing how it gravitationally perturbs nearby stars

This suggests to me that others might want to look into the goings-on in the Trapezium cluster to see if the high velocity of the stars there can only be explained by a black hole, or if there is some other explanation.

But perhaps everybody who might look into it are just busy doing other things, because it would be too hard or frustrating to measure the velocity of the stars there and find out something definite about a possible black hole in the Orion Nebula.

Ann

[Ann]

Fossils are not really that easy to find. Chances of losing remains to entropy through various forces are pretty high. There is a pretty good chance there are no large fossils of any sort below Ann's house. Perhaps I should have created a better metaphor...

Well, who knows? A high school student just recently found some remains of a predatory dinosaur some sixty miles from where I live. Who's to say there is nothing under my house?

However, I live in a condo, so it's not just my house. And you would have to deal with all the others in my condo if you wanted to dig a hole below it.

Ann

[Chris Peterson]

I defer to your superior knowledge on this Chris, but my thinking was informed by a response that Dr. Monica Young gave to myself and others in the comments to the S&T news story she wrote back in 2012 on their website. Readers like myself had asked, 'if there was a >100M_SUN black hole in the ONC, wouldn't it have produced detectable evidence?' Her response was:

There are some great questions here, and hopefully the following will answer a few of the outstanding questions: If there is a black hole in the Orion Nebula Cluster, it’s unlikely that it’s accreting much gas.

But there's every reason to think it would go through periods of accretion. If so, we could probably detect it. So it's something to look for.

So it won’t emit many X-rays from its accretion disk, and it won’t form jets strong enough for us to see. That’s why the main test for its existence is the motion of stars in the very inner core of the cluster, which requires a higher degree of resolution than what’s been done in the past.

Sure. But not higher than we're instrumentally capable of.

So to answer your question Chris to me "direct evidence" would be signs of accretion disk and/or jet effects and/or the motions of inner core stars that Dr. Young mentioned, whereas "indirect evidence" could be stellar motions of a much broader category like the runaway stars that were described in the above Jim Kaler quote, as well as the absence of the expected numbers of OB stars that Subr's BH theory attempts to explain.

Okay, that was my question. I'd consider both observation of an accretion disc or orbital perturbations to be equally direct evidence. I'd be inclined to consider runaway stars to be indirect, since it's doubtful that their presence could only be caused by a black hole. Such evidence would be ambiguous.

[geckzilla]

But there's every reason to think it would go through periods of accretion. If so, we could probably detect it. So it's something to look for.

One wonders if we would even catch it. I'm under the impression there are frequent holes in the monitoring of the sky in X-rays since there is only ever one or two telescopes doing it at any one time. It's not like supernovas where even amateur telescopes can help look.

[BDanielMayfield]

But there's every reason to think it would go through periods of accretion. If so, we could probably detect it. So it's something to look for.

One wonders if we would even catch it. I'm under the impression there are frequent holes in the monitoring of the sky in X-rays since there is only ever one or two telescopes doing it at any one time. It's not like supernovas where even amateur telescopes can help look.

Chris' comment there makes me wish to recant my "it will be well neigh impossible to actually see direct evidence of an ONC BH for the foreseeable future" statement. I most definitely agree that it is something to look for.

And a lot of eyes are looking too, as this is the brightest and easiest to find nebula in the whole sky. I wonder though, are X-rays the only way this might be spotted (other than gravitational motions of other stars)? Don't BH accretion discs radiate all across the EM spectrum? With people (from pros on down) always looking this way, even a transient event might be caught if it was in visible, IR or some other part of the EM band.

Bruce