E0 galaxy 13 Januari 2011
Posted by azmirul in Astronomy, Link menarik.
Tags: e0 galaxy, galaxy classifaction, sphere galaxy
Dulu aku tertanya-tanya ada atau tidak galaxy yang berbentuk sphere macam bola sebab selalu kita dengar adalah berbentuk ellipsoid lonjong dan lagi satu spiral galaxy yang selalunya berbentuk disc yang leper… sebenarnya ada iaitu yang diklasifikasikan sebagai E0 galaxy.. Berdasarkan hubble classification, elliptical galaxy ditulis/ diklasifikasikan sebagai “En” iaitu value “n” antara E0 – E7 dan nilai n adalah merujuk kadar berapa keleperan galaxy tersebut. Jadi, E0 galaxy adalah merujuk kepada galaxy yang berbentuk hampir bulat seperti bola (almost sphere ellipsoid shape)… antara E0 galaxy yang terkenal adalah Messier 87 dan Messier 89… (disclaimer: ada juga yang mengatakan bentuk galaxy yang dijumpai kelihatan berbentuk bulat dari bumi ini mungkin juga berbentuk elliptical lonjong dari padangan lain).
Messier 87 (source: Wikipedia)
Messier 89 (source: Wikipedia)
Edwin Hubble's Classification (source: Wikipedia)
why is our galaxy a disc and not a sphere?
In the modified Hubble sequence galaxy morphological classification scheme of French astronomer Gérard de Vaucouleurs, Messier 87 is categorized as an E0p galaxy. The E0 designation is used for an elliptical galaxy that displays no flattening—that is, it appears spherical in profile. A ‘p’ suffix indicates a peculiar galaxy that does not fit cleanly into the classification scheme; in this case, the peculiarity is caused by the presence of a relativistic jet emerging from the core.
Current observations indicate that M89 may be nearly perfectly spherical in shape. This would be unusual as all other known elliptic galaxies are relatively elongated ellipsoids. However, it is possible that the galaxy is oriented in such a way that it appears spherical to an observer on Earth but is in fact elliptical.
It should be noted that the apparent shape of an elliptical galaxy in the sky is more dependent on our line-of-sight to that galaxy than any intrinsic properties of the galaxy itself. If a galaxy were intrinsically cigar shaped, and we viewed it edge-on, it would appear circular.
The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1936. It is often known colloquially as the “Hubble tuning-fork” because of the shape in which it is traditionally represented.
It has been theorized that an elliptical galaxy will result from a merger of the two spirals.
Every bright elliptical galaxy is believed to contain a supermassive black hole at its center.
Spiral galaxies are named for the (usually two-armed) spiral structures that extend from the center into the disk. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disk because of the young, hot OB stars that inhabit them.
The most massive galaxies in the sky are giant elliptical galaxies. Their stars are on orbits that are randomly oriented within the galaxy (i.e. they are not rotating like disk galaxies). They are composed of old stars and have little to no dust. All elliptical galaxies probed so far have supermassive black holes in their center, and the mass of these black holes is correlated with the mass of the elliptical galaxy. They are also correlated to a property called sigma which is the speed of the stars at the far edge of the elliptical galaxies. Elliptical galaxies do not have disks around them, although some bulges of disk galaxies look similar to elliptical galaxies. One is more likely to find elliptical galaxies in more crowded regions of the universe (such as galaxy clusters).