Help! My stars are leaking!

Sep 16, 2011 By Jon Voisey, Universe Today
A fast-moving star, Alpha Camelopardalis, creates a stunning bow shock in this new image from WISE. Credit: NASA/JPL-Caltech/WISE Team

Star clusters are wonderful test beds for theories of stellar formation and evolution. One of the key roles they play is to help astronomers understand the distribution of stellar masses as stars form (in other words, how many high mass stars versus intermediate and low mass stars), known as the Initial Mass Function (IMF). One of the problems is that this is constantly evolving away from the initial distribution as stars die or are ejected from the cluster. As such, understanding these mechanisms is essential for astronomers looking to backtrack from the current population to the IMF.

To assist in this goal, astronomers led by Vasilii Gvaramadze at the University of Bonn in Germany are engaged in a study to search young clusters for stars in the process of being ejected.

In the first of two studies released by the team so far, they studied the cluster associated with the famous . This nebula is well known due to the famous “Pillars of Creation” image taken by the aging Hubble Space Telescope which shows towers of dense gas currently undergoing star formation.

Two main methods exist for discovering stars on the lam from their birthplace. The first is to examine stars individually and analyze their motion in the plane of the sky (proper motion) along with their motion towards or away from us (radial velocity) to determine if a given star has sufficient velocity to escape the cluster. While this method can be reliable, it suffers because the clusters are so far away, even though the stars could be moving at hundreds of kilometers per second, it takes long periods of time to detect it.

Instead, the astronomers in these studies search for runaway stars by the effects they have on the local environment. Since young clusters contain large amounts of gas and dust, stars plowing through it will create , similar to those a boat makes in the ocean. Taking advantage of this, the team searched the Eagle Nebula cluster for signs of bow shocks from these stars. Searching images from several studies, the team found three such bow shocks. The same method was used in a second study, this time analyzing a lesser known cluster and nebula in Scorpius, NGC 6357. This survey turned up seven bow shocks of stars escaping the region.

In both studies, the team analyzed the spectral types of the stars which would indicate their mass. Simulations of nebulae suggested that the majority of ejected stars are given their initial kick as they have a close pass to the center of a cluster where the density is the highest. Studies of clusters have shown that their centers are often dominated by massive O and B spectral type stars which would mean that such stars would be preferentially ejected. These two studies have helped to confirm that prediction as all of the stars discovered to have bow shocks were massive stars in this range.

While this method is able to find runaway stars, the authors note that it is an incomplete survey. Some stars may have sufficient velocity to escape, but still fall under the local sound speed in the nebula which would prevent them from creating a bow shock. As such, calculations have predicted that roughly 20% of escaping stars should create detectable bow shocks.

Understanding this mechanism is important because it is expected to play the dominant role in the evolution of the mass distribution of clusters early in their life. An alternative method of ejection involves stars in a binary orbit. If one star becomes a supernova, the sudden mass loss suddenly decreases the gravitational force holding the second star in orbit, allowing it to fly away. However, this method requires that a cluster at least be old enough for to have evolved to the point they explode as supernova, delaying this mechanism’s importance until at least that point and allowing the gravitational sling-shot effects to dominate early on.

Explore further: How baryon acoustic oscillation reveals the expansion of the universe

add to favorites email to friend print save as pdf

Related Stories

Young stellar clusters

Jan 17, 2011

(PhysOrg.com) -- Most stars are thought to form in clusters rather than in isolation, as the gas and dust in a molecular cloud coalesces under the influence of gravity until clumps develop that are dense enough ...

The Chandra Carina complex project

May 16, 2011

(PhysOrg.com) -- The Great Nebula in the constellation of Carina is a massive star-forming complex located about 7.5 thousand light-years away. The main star in the complex, Eta Carinae, shines brightly in ...

Hubble Sees Star Cluster 'Infant Mortality'

Jan 10, 2007

Astronomers have long known that young or "open" star clusters must eventually disrupt and dissolve into the host galaxy. They simply don't have enough gravity to hold them together, unlike their much more ...

Young Star Clusters

Oct 12, 2009

(PhysOrg.com) -- Most stars form in clusters. Recent studies of nearby star forming regions find that about three-quarters of their young stars are located in groups with ten or more members. The formation ...

Image: Starburst Cluster Shows Celestial Fireworks

Jul 06, 2010

(PhysOrg.com) -- Like a July 4 fireworks display, a young, glittering collection of stars looks like an aerial burst. The cluster is surrounded by clouds of interstellar gas and dust—the raw material for ...

Recommended for you

The Great Cold Spot in the cosmic microwave background

17 hours ago

The cosmic microwave background (CMB) is the thermal afterglow of the primordial fireball we call the big bang. One of the striking features of the CMB is how remarkably uniform it is. Still, there are some ...

Mystery of rare five-hour space explosion explained

Sep 17, 2014

Next week in St. Petersburg, Russia, scientists on an international team that includes Penn State University astronomers will present a paper that provides a simple explanation for mysterious ultra-long gamma-ray ...

User comments : 6

Adjust slider to filter visible comments by rank

Display comments: newest first

omatumr
1 / 5 (5) Sep 16, 2011
Star clusters are wonderful test beds for theories of stellar formation and evolution.


Thanks for the story.

I look forward to the time when studies like these will be able to decide if

a.) Stars from by the collapse of an interstellar cloud of hydrogen

b.) The pulsar cores of stars generate a cloud of hydrogen by
_b1. Neutron emission, followed by
_b2. Neutron decay to hydrogen [1,2]

With kind regards,
Oliver K. Manuel
Former NASA Principal
Investigator for Apollo

1. "Is the Universe Expanding?" The Journal of Cosmology 13, 4187-4190 (2011):

http://journalofc...102.html

2. ""Neutron Repulsion", The APEIRON Journal, in press (2011):

http://arxiv.org/...2.1499v1
jamesrm
3.4 / 5 (5) Sep 16, 2011
frajo
2 / 5 (8) Sep 16, 2011
http://mominer.mst...

You, jamesrm, are an anonymous coward who acts in a non-consensual way towards victims unknown to you by permanently reminding them of their pain in moments when they don't want to be reminded by a person unknown to them.

You don't think, you don't care; you are driven by your dissocial needs.
And victims know about the meaning of complementary behaviour.
jsdarkdestruction
3 / 5 (4) Sep 17, 2011
aww, frajo got upset again. Get over it. You cant accept oliver is a child molester? are you one too? maybe one in the closet like oliver was all those years?
jsdarkdestruction
3.7 / 5 (3) Sep 17, 2011
Alright,After some time thinking about it I'll say this- frajo
"are you one too? maybe one in the closet like oliver was all those years?"
That part was uncalled for. I'm sorry.
Ethelred
3.9 / 5 (7) Sep 17, 2011
A few selected questions that Oliver is pretending aren't relevant.

Where is someone, someone remotely competent as opposed to the South African geologist, that supports your idea that the Sun is a pulsar? And how can a pulsar form IF there is such a thing as neutron repulsion?

How could degenerate matter form with that going on keeping in mind your contradictory claim that neutron repulsion makes Black Holes impossible despite the math not working for you at all?


Oliver seems to have freaked out again. After running away from multiple threads where he refused to answer legitimate, relevant questions he has spammed another half dozen or so threads with his Crankery.

Ethelred