Study finds open cluster NGC 2682 at least two times larger than previously thought

Study finds open cluster NGC 2682 at least two times larger than previously thought
NGC 2682. Credit: 2MASS/UMass/IPAC-Caltech/NASA/NSF

Based on new data from ESA's Gaia satellite, astronomers have provided more insights into properties of the nearby open cluster NGC 2682, revealing that its size is at least two times greater than previously believed. The findings are detailed in a paper published May 6 on the arXiv pre-print repository.

Located some 2,800 light years away, NGC 2682 (aka Messier 67, or M67 for short) is an in the constellation of Cancer. With an estimated age of about 3.6 billion years, it is one of the nearest old open clusters. Notably, its age and initial is similar to that of the sun, hence astronomers even considered that the sun might actually have originated from NGC 2682.

Published about one year ago, the latest catalog of data from Gaia satellite (known as Data Release 2, or DR2) provides high-precision measurements, including positions in the sky, parallaxes and proper motions for more than 1 billion sources in the Milky Way. The release contains collected by Gaia in the timespan of nearly two years – between July 25, 2014 and May 23, 2016.

DR2 has the potential of revealing more insights into the nature of NGC 2682 as astrometric information in this release could be a to investigate extra-tidal regions of several open clusters in the solar neighborhood. So a team of European astronomers led by Ricardo Carrera of Astronomical Observatory of Padova in Italy recently decided to use DR2 in order to learn more about NGC 2682.

In particular, the researchers investigated the spatial distribution of this of stars in order to constrain its dynamical evolution. Given that most open clusters should dissolve at an age of around 1 billion years, the fact that NGC 2682 survived until now suggests that it was likely much more massive in the past and has an interesting dynamical history.

"We use Gaia DR2 data to identify NGC 2682 members up to a distance of about 150 pc (10 degrees). Two methods (Clusterix and UPMASK) are applied to this end. We estimate distances to obtain three-dimensional stellar positions using a Bayesian approach to parallax inversion, with an appropriate prior for star clusters," the paper reads.

The main conclusion from the study conducted by Carrera's team is that NGC 2682 is at least twice as large than previously thought. Based on the DR2 data, the astronomers found that this cluster extends up to approximately 160 light years, while other observations carried out in the recent years suggested not more than 78 .

Furthermore, the study confirmed that NGC 2682 is mass-segregated with the most massive objects concentrated in the central regions. However, there are also stars outside the tidal radius of this cluster. The researchers assume that these extra-tidal stars in NGC 2682 may originate from external perturbations such as disk shocking or dynamical evaporation from two-body relaxation. They also plan more studies of the cluster to test these scenarios.


Explore further

Observations uncover details about the open cluster IC 4996

More information: R. Carrera, et al. The extended halo of NGC 2682 (M 67) from Gaia DR2. arXiv:1905.02020v1 [astro-ph.SR] arxiv.org/abs/1905.02020

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Citation: Study finds open cluster NGC 2682 at least two times larger than previously thought (2019, May 15) retrieved 18 September 2019 from https://phys.org/news/2019-05-cluster-ngc-larger-previously-thought.html
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May 15, 2019
If they still think that our Sun originated from that cluster then it actually spreads some 2800 LY rather than just 160 LY. If we came from that cluster then we are part of it's spread, right, so if we are 2800 LY from the cluster, then it is spread out at least that far, and not just a measly lil 160 LY.

Unless they consider this proof that Sol is Not from that open cluster.

May 15, 2019
If we came from that cluster then we are part of it's spread, right,
No, because the theory considered here (which I have no personal opinion on whether it is correct) is that our Sun might have left the cluster i.e. 'escaped' it via gravitational interactions and possibly as it passed very close to a star in the milky way as the cluster passed through the milky way. It is believed (and for good reason) that stars in clusters sometimes do do that i.e. escape from clusters via gravitational interactions.

RNP
May 15, 2019
@Steelwolf
If they still think that our Sun originated from that cluster then it actually spreads some 2800 LY rather than just 160 LY. If we came from that cluster then we are part of it's spread, right, so if we are 2800 LY from the cluster, then it is spread out at least that far, and not just a measly lil 160 LY.


Not so. Observations show that *some* stars are ejected from star clusters at relatively high velocities. After several galactic rotations (about 20 since the Sun was formed) such stars can end up at very large distances from their parent cluster. The others, still bound to the cluster, remain in much closer proximity.

RNP
May 15, 2019
@Humy
Oops. You just beat me to it!

May 15, 2019
This is one of those "filling in the gaps" exercises that make up real science. Nothing amazing here, just standard plodding along. This is the heart of science.

May 15, 2019
Even being 'Ejected' is a spreading movement of the formation, yes, only a small fraction expand this far from the cluster, but IFF we come from that cluster than WE would be still within it's actual spread. A small percentage of that spread, yes, but we would still be a spread portion of that cluster by definition. Ejection spreads the matter out farther, is all. Part of the overall dissolving of the cluster into the galaxy.

RNP
May 15, 2019
@Steelwolf
This was answered by both Humy and myself above. It is not a "simple spreading movement". Once a star has been freed from the gravity of its parent cluster, it can separate by huge distances , while those still bound remain in the cluster.

If you don't want to listen to or think about the answers people give you, there is no point in asking the questions.

May 15, 2019
You do not seem to understand the difference between stating a FACT, as I have, of definition: If A comes from Group B then however far A goes, that is how far, at a minimum, that B has spread.

I understand the basic connotation of 'the intact cluster' but IFF (used the mathematically If and Only If) we come from that cluster then we are STILL a portion of that cluster, no matter how far separated, it is part of the natural, mathematically backed spread, and a matter of definition of the intact cluster.

But in reality, if we are from said cluster, we are at the minimum spread of that cluster. not even the maximum, even though we may no longer show cohesive movement with said cluster.

Drop a handful of marbles on the ground, even low carpet, there will be a primary 'cluster' and there will be 'spread' as they bounce apart and roll, but they ALL came from the same cluster that was dropped.

That is the point I make, their artificial distinction of boundary to the remaining cluster.

RNP
May 15, 2019
@Steelwolf
OK. So you INSIST on not listening or thinking about the answers you are given. Just be aware that that is why you still do not understand the paper under discussion.

May 15, 2019
I do, very totally, understand the paper in question. I also understand the nature of open clusters, and it shows it as being mass segregated but also need to look at what follows that:
"However, there are also stars outside the tidal radius of this cluster. The researchers assume that these extra-tidal stars in NGC 2682 may originate from external perturbations such as disk shocking or dynamical evaporation from two-body relaxation."

We are just so very far so as to not be 'considered as to be' a part of that cluster still, and yes, considered to be dissolved into the Milky Way galaxy, but we are still a part of that cluster, no matter how far spread apart from it. Their big finding was "Stars outside the tidal radius"...we are just well beyond and escaped from said tidal radius, but IFF we were a part of said cluster, then we are just a very far dissipated portion, well dissolved into the MW, but our chemical and physical beginnings would place us as part of that cluster even now.

May 15, 2019
You do not seem to understand the difference between stating a FACT, as I have, of definition: If A comes from Group B then however far A goes, that is how far, at a minimum, that B has spread.

I understand the basic connotation of 'the intact cluster' but IFF (used the mathematically If and Only If) ...
Using a biconditional only adds pendantry to the error, as does the mystification of 'mathematically based spread' (WUT). In fact, there was so much bafflegab in that defense I can only assume our leg is being pulled.

May 15, 2019
I understand that they are talking about a stable, cohesive unit with the open cluster. What I find so funny is them saying that 160 ly is the farthest scattering, yet they also stated that 'some' astronomers 'had thought' that our Sun was at one point part of that cluster due to chemical matches, and yet the basic term of scattering would have to include us as still part of that object, even though we are merging into a larger object. So while the visible Core of that cluster may be 160 LY, IFF we were formed as part of it then we are a literally 'scattered portion' of the cluster. Yet it is some 2800 LY from us, so if we came from there, then we are part of it's scattering And part of the MW.

Would have been better to state that it's visible core is of that size (160LY) and not mentioned being possibly from there. If maximum scattering is held to visible size then that would have left out stars on possible long slow loop orbits still held by it's gravity, but not visibly within it.

May 15, 2019
What I find so funny is them saying...

Would have been better to state that it's visible core is of that size (160LY) and not mentioned being possibly from there. If maximum scattering is held to visible size then that would have left out stars on possible long slow loop orbits still held by it's gravity, but not visibly within it.
Now, on to the important stuff:
*What I find so funny is their saying...
*...its visible core...
*...its gravity,...

May 16, 2019
@SteelWolf, a star is part of a cluster if it is gravitationally bound to that cluster. If, due to gravitational interaction with other members of the cluster, the star acquires a velocity greater than the cluster's escape velocity (happens quite often in globular clusters), that star will no longer be gravitationally bound to the cluster and will leave the cluster. Thereafter, no matter how close or far it may be when observed, it is no longer part of the cluster.

Think of the many spacecraft that have been launched from Earth into "deep space" - once the velocity of those craft exceeded escape velocity from the Earth (a necessary condition for them to go boldly forth), they were no longer part of the Earth+satellites system.

It's all down to gravitational binding energy - if it's negative, you're in, if it's positive, you're out.

May 16, 2019
@SW
What I find so funny is them saying that 160 ly is the farthest scattering
Read the article here in phys.org, and then the paper referred to. Nowhere will you read the word "scattering" being used: only you are using the word when referring to what the authors describe as "the spatial distribution of NGC 2682 stars".

Earlier estimates of the cluster's size were based on fairly inaccurate estimations, from various star catalogues, of distances and velocities of stars appearing close to the cluster in the plane of the sky. With the release of the much more accurate Gaia DR2 datasets, much better estimates of distances and velocities can be made, such that this latest estimate of the cluster's extent turns out to be roughly twice as great as previously thought. Meaning the mass of the cluster is several times larger than previously thought.

May 16, 2019
Noy sure of the point of this disagreement?
Can we at least agree that collecting new data, correcting previous errors
& developing better methodology?
Forces all of us to change our assumptions of what we thought we had known?

After all, none of this comes down to us carved in stone!

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