The enigma of the missing stars in space may be solved

Nov 18, 2010

In the local group of galaxies, there are about 100 billion stars. According to astronomers' calculations, there should be many more. Now, physicists from the University of Bonn and the University of St. Andrews in Scotland may have found an explanation for this discrepancy. Their study will appear in the upcoming issue of the Monthly Notices of the Royal Astronomical Society.

New are born in the around the clock – on the Milky Way, currently about ten per year. From the birth rate in the past, we can generally calculate how populated space should actually be. But the problem is that the results of such calculations do not match our actual observations. "There should actually be a lot more stars that we can see," says Dr. Jan Pflamm-Altenburg, astrophysicist at the Argelander-Institut für Astronomie of the University of Bonn.

So, where are those stars?

For years, astronomers worldwide have been looking for a plausible explanation for this discrepancy. In cooperation with Dr. Carsten Weidner from St. Andrews University, Dr. Pflamm-Altenburg and Professor Dr. Pavel Kroupa, Professor of Astrophysics at the University of Bonn, may now have found the solution. It seems that so far, the birth rate has simply been overestimated. But this answer is not quite as simple as it sounds. Apparently, the error of estimation only occurs during periods of particularly high star production.

The reason for this lies in the manner in which astronomers calculate the birth rate. "For the local Universe – i.e., the Milky Way as our home and the adjacent galaxies – it is relatively simple," explains Professor Kroupa. "Here we are able to count the young stars one by one, using huge telescopes."

The problem with this method is that it only works for our immediate vicinity. But many galaxies are so distant that even the best telescope simply overlooks their small stars. As luck would have it, however, occasionally there is an especially large whopper among the newbie's in the sky. Such a star will, even if it cannot be directly discovered as an individual star, leave its traces in the light of even the farthest galaxies. The number of large whoppers then determines the strength of this trace.

In our immediate vicinity, these large whoppers occur with a fixed probability. There are always about 300 lightweights to one "big star baby." This numerical ratio seemed to be universal. So it was sufficient for astronomers to know the number of the large whoppers, for this allowed them to determine the number of new-born stars by simply multiplying the former number by a factor of 300.

Population explosion in space

Recently, however, some Bonn astronomers around Professor Kroupa began doubting the fixed ratio. Their hypothesis is that at times when the galactic nurseries are booming, they generate a considerably higher number of stellar heavies than normal. The reason for this, according to this theory, is so-called stellar crowding. For stars are not single children; they are born in groups, as so-called star clusters. At birth, these clusters are always of a similar size – no matter whether they contain 100 star embryos - or 100,000.

Consequently, at times of a high birth rate, space can be at a premium in star clusters. Astronomers call such galaxies that are particularly rich in mass "ultra-compact dwarf galaxies," or UCD's for short. In these, things are so tight that some of the young stars fuse during formation. Thus, more stars rich in mass than normal emerge. The "small to large" ratio is then only about 50 to 1. "In other words, we used to estimate the number of newly formed small stars by far too high," explains Dr. Carsten Weidner.

The researchers from Bonn and St. Andrews have now corrected the birth rates according to the projections of the stellar crowding theory. With an encouraging result – they actually arrived at the number of stars that can be seen today.

Explore further: When did galaxies settle down?

More information: Paper online: arxiv.org/abs/1011.3814

add to favorites email to friend print save as pdf

Related Stories

Stars cheek by jowl in the early Universe

Feb 12, 2009

(PhysOrg.com) -- In the early Universe, some galaxies may have had stars packed together a hundred times more closely than in the present day, according to research by a University of Bonn team to be published ...

Baby booms and birth control in space

Sep 25, 2007

Stars in galaxies are a bit similar to people: during the first phase of their existence they grow rapidly, after which a stellar birth control occurs in most galaxies. Thanks to new observations from Dutch ...

Antennae Galaxies

May 19, 2008

This image of the Antennae galaxies is the sharpest yet of this merging pair of galaxies. During the course of the collision, billions of stars will be formed. The brightest and most compact of these star ...

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 ...

Colliding galaxies make love, not war

Oct 17, 2006

A new Hubble image of the Antennae galaxies is the sharpest yet of this merging pair of galaxies. As the two galaxies smash together, billions of stars are born, mostly in groups and clusters of stars. The ...

Alien invaders pack the Milky Way

Feb 23, 2010

(PhysOrg.com) -- Around a quarter of the globular star clusters in our Milky Way are invaders from other galaxies, new research from Swinburne University of Technology (Australia) shows.

Recommended for you

Hubble sees 'ghost light' from dead galaxies

13 hours ago

(Phys.org) —NASA's Hubble Space Telescope has picked up the faint, ghostly glow of stars ejected from ancient galaxies that were gravitationally ripped apart several billion years ago. The mayhem happened ...

When did galaxies settle down?

20 hours ago

Astronomers have long sought to understand exactly how the universe evolved from its earliest history to the cosmos we see around us in the present day. In particular, the way that galaxies form and develop ...

Image: Hubble views the whirling disk of NGC 4526

21 hours ago

This neat little galaxy is known as NGC 4526. Its dark lanes of dust and bright diffuse glow make the galaxy appear to hang like a halo in the emptiness of space in this image from the NASA/ESA Hubble Space ...

Planet-forming lifeline discovered in a binary star system

Oct 29, 2014

Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) have detected a streamer of dust and gas flowing from a massive outer disk toward the inner reaches of a binary star system. This never-before-seen ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

omatumr
1 / 5 (2) Nov 20, 2010
The Enigma of Missing Stars probably means that other stars recycle, just as the star did that gave birth to the solar system.

See: Scientific Genesis: 1. Origin of the Solar System
http://www.youtub...e_Qk-q7M

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

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.