What is the difference between galactic and globular clusters

That indicates the younger clusters may have been formed during a merger with other galaxies , and the older clusters may be relics from when the Milky Way was born. The stars in globular clusters are packed in much more tightly than in any other place in a galaxy. That leads to the creation of binary systems, including those with compact objects: white dwarfs, neutron stars , and black holes. Theoretical calculations show that exotic binaries, such as white dwarf-neutron star pairings, happen about times more often than in the rest of the galaxy.

Many of these systems are potential sources for LIGO and future gravitational wave observatories. X-ray observations of clusters have revealed many of these binary systems, which include low-radiation quiescent low-mass X-ray binaries qLMXBs , which are ordinary stars paired with neutron stars that pull matter from their companions into a hot accretion disk.

Some neutron stars in binaries are millisecond pulsars MSPs , objects that rotate hundreds of times every second. Stars in open clusters likely formed at nearly the same time from the same nebula. These clusters are much smaller than globular clusters, containing dozens or hundreds of stars, and they fall into irregular rather than spherical shapes.

Open clusters are typically younger than globulars, too, and often are rich in gas between the stars. The Milky Way is home to more than 1, known open clusters, but astronomers think the actual number could be ten times higher.

The location of open clusters means passing stars and other objects tend to pull them apart over long periods of time. For that reason, most open clusters in the Milky Way are less than a billion years old, with older clusters located farther away from the galactic center. Open clusters are important laboratories for understanding star evolution, since they are home to relatively young stars as a rule.

Open clusters provide one means to measure distances in space. For stars in middle-age, the mass determines the color of a star: heavier stars are brighter and bluer, while lower-mass stars are redder. Mapping the apparent brightness of the stars of each color in a cluster and comparing it to the known amount of light emitted by those stars provides a way of knowing how far that light traveled to reach us.

The youngest star clusters are embedded clusters: groups of stars swathed in interstellar gas and dust. While a typical galaxy contains billions of stars, a number of tiny galaxies have been found in recent years that do not fit the classic picture and instead resemble the groups of stars known as star clusters.

So which are they? To try and settle the matter, Kroupa and Duncan Forbes of Swinburne University of Technology in Hawthorn, Victoria, Australia, have launched an online survey to poll astronomers on what they think the defining features of a galaxy should be. Star clusters and galaxies both contain stars bound together by gravity, but while the members of a star cluster are thought to form simultaneously from a collapsing ball of gas, galaxies have richer histories.

Is mass a requirement to make the distinction? I am curious if mass is an absolute requirement. Stars can vary in mass, but do not become different things. Also, both references were extremely interesting. Thank you! Isn't it more correct to note that when we look at things that have historically been classed as a galaxy or a cluster, and we look at how much dark matter appears to be associated with them, we see a correlation?

While we might now use a measure of dark matter present to make a distinction in otherwise unclear cases, surely the amount of gas and the ages of the stars present will be more relevant in the classification of an object? Do we know any instances of free-standing astronomical objects of the mass of globular clusters that don't have the dark-matter requirements of dwarf galaxies?

Stars are a different case - they are discrete packages of gas which at one point either collapsed due to an overdensity in a region or did not because it simply didn't have enough mass I know there are other effects here that determine star fomation; from a purely Newtonian perspective, I think my statement is not unreasonable.

Since DM doesn't interact electromagnetically, it was able to cool off and form overdensities for which baryons would later fall into - basically, the baryons do trace the dark matter. For a sufficiently massive dark matter overdensity, it is able to collect enough gas for there to be a galaxy within; for smaller overdensities, there may not be enough gas within to form a galaxy, and to that end, there may not be enough to even form any stars.

This is the idea behind dark companion galaxies, and has been proposed as a solution to the 'missing halo problem'. Show 4 more comments. Jeremy Jeremy 3, 14 14 silver badges 31 31 bronze badges. It appears that some, maybe most but not necessarily all astronomy. And there is no intrinsic difference between a star cluster and a galaxy?

I said they may not be clearly distinct groups, not 'the same thing'. That is, it may be difficult to tell in a few cases if one is one or the other. But generally, they will be catalogued as either a globular or a dwarf spheroidal galaxy. Watch : Mining the Moon for rocket fuel. Queen guitarist Brian May and David Eicher launch new astronomy book. Last chance to join our Costa Rica Star Party! Learn about the Moon in a great new book New book chronicles the space program.

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