ESO/MPE: Unexpected Excess of Giant Planets in Star Cluster

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ESO/MPE: Unexpected Excess of Giant Planets in Star Cluster

Post by bystander » Fri Jun 17, 2016 3:09 pm

Unexpected Excess of Giant Planets in Star Cluster
Max Planck Institute for Extraterrestrial Physics
European Southern Observatory | 2016 Jun 17
[img3="Wide-field View of the Open Star Cluster Messier 67
Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin
"]https://cdn.eso.org/images/screen/eso1402c.jpg[/img3][hr][/hr]
An international team of astronomers have found that there are far more planets of the hot Jupiter type than expected in a cluster of stars called Messier 67. This surprising result was obtained after long-term observations using a number of telescopes and instruments, which led to the discovery of three giant planets. The denser environment in a cluster will cause more frequent interactions between planets and nearby stars, which may explain the excess of hot Jupiters.

The international team led by Roberto Saglia at the Max Planck Institute for Extraterrestrial Physics and Luca Pasquini at ESO has spent several years collecting high-precision measurements of 88 stars in Messier 67. This open star cluster is about the same age as the Sun and it is thought that the Solar System arose in a similarly dense environment.

The team used HARPS at the ESO La Silla 3.6m telescope as well as the High Resolution Spectrograph on the Hobby-Eberly Telescope in Texas, USA, to look for the signatures of giant planets on short-period orbits, hoping to see the tell-tale “wobble” of a star caused by the presence of a massive object in a close orbit, a kind of planet known as a hot Jupiters. This hot Jupiter signature has now been found for a total of three stars in the cluster alongside earlier evidence for several other planets. ...

The study found that hot Jupiters are more common around stars in Messier 67 than is the case for stars outside of clusters. ...

Search for Giant Planets in M67 III: Excess of Hot Jupiters in Dense Open Clusters - A. Brucalassi et al
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Unexpected presence of bright blue B-type star in 4 billion year old cluster

Post by Ann » Fri Jun 17, 2016 6:11 pm

M67, the four billion year old cluster whose member stars are somewhat similar to the Sun in terms of metallicity, is home to an astounding bright blue B-type star of spectral class B8. How did a massive blue B-type star consume its core hydrogen at a prodigious rate for four billion years without running out of hydrogen in its core?

The most likely answer is that the star, HIP 43465, is a blue straggler, the merger product of two smaller stars. Alternatively, it might be an Algol, where one star siphons off material from another one.

In any case, I find this blue star remarkable. You can see it in the picture above at the bottom of the concentrated core of the cluster (many of the bright outliers are also probable members of the cluster, or at least they seem to have comparable proper motion).

Fascinating!

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Re: ESO/MPE: Unexpected Excess of Giant Planets in Star Cluster

Post by rstevenson » Fri Jun 17, 2016 8:43 pm

The item says...
This open star cluster is about the same age as the Sun and it is thought that the Solar System arose in a similarly dense environment.
But it is also thought that the stars formerly in the cluster with our Sun have long ago drifted away from our vicinity. In fact, they've drifted so far away during our roughly 20 orbits of the Milky Way that we can't even be sure we've identified any of them. So if this cluster is the same age, why hasn't it simlarly difted apart?

Rob

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Re: ESO/MPE: Unexpected Excess of Giant Planets in Star Cluster

Post by Ann » Sat Jun 18, 2016 5:20 am

rstevenson wrote:The item says...
This open star cluster is about the same age as the Sun and it is thought that the Solar System arose in a similarly dense environment.
But it is also thought that the stars formerly in the cluster with our Sun have long ago drifted away from our vicinity. In fact, they've drifted so far away during our roughly 20 orbits of the Milky Way that we can't even be sure we've identified any of them. So if this cluster is the same age, why hasn't it simlarly difted apart?

Rob
It has to do with the cluster's richness and self-gravity, but still more with its location. I once read a hugely interesting ARXIV paper about globular clusters and why they haven't drifted apart after 10-12 billion years. According to that paper, the globular clusters formed naturally out of the huge molecular clouds that were present back then in galaxies (and perhaps out of the galaxies, too). But the same molecular clouds that formed the globulars also destroyed them. A sufficient number of collisions with giant gas clouds disrupted the globulars.

But according to the same paper, interactions between galaxies could fling some globulars into elliptical orbits in the halos of the galaxies. There were no giant molecular clouds in the halos, and the globulars didn't face sudden wholesale destruction anymore. They just kept slowly shedding stars due to natural orbital interactions betwen their member stars.

As for M67, it is rich. But more importantly, it is located in a sparsely populated part of our galaxy, in one of the outer arms, unless I'm very much mistaken. It has therefore very rarely collided with molecular clouds, a cosmic jam phenomenon that is just now happening to the Pleiades Cluster.

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Re: ESO/MPE: Unexpected Excess of Giant Planets in Star Cluster

Post by rstevenson » Sat Jun 18, 2016 12:23 pm

Ah yes, I should have known that. As they say in the real estate biz, location, location, location.

Thanks Ann.

Rob

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