Lens-shaped galaxies have characteristics astronomers see in elliptical and spiral galaxies
Space news (lenticular galaxies) – 50 million light-years from Earth, in the constellation of Canes Venatici (The Hunting Dogs) –
This Hubble Space Telescope image of lenticular galaxy NGC 4111 shows an island universe with a more chaotic past than first thought. Lenticular or lens-shaped galaxies are labelled S0 on the Hubble Tuning Fork and are classified as a transitional type between spiral and elliptical galaxies.
Lenticular galaxies host older stars as observed in elliptical galaxies and include a disc as seenin spiral galaxies. However, they have a bulge and thin disc, which hasn’t been observed in elliptical galaxies. They also don’t have arms and the gas and dust detected in spiral galaxies.
NGC 4111 appears as a thin sliver of lights in this image because Hubble’s viewing the edge of the galaxy. At first glance, this island universe looks relatively quiet, but there are regions suggesting a more chaotic past. Pillars of dark filaments silhouetted against the bright core of the galaxy and running through the centre at right angles to the thin disc. Dark filaments of dust and gas astronomers associate with a ring of materialorbiting its core.
This ring of orbiting material isn’t aligned with the main disc of NGC 4111, which has astrophysicists thinking it could be the remains of a smaller galaxy it collided with long ago. Considering the possible mass and volume of this past meal, indigestion probably isn’t unexpected.
Hints of a spiral structure embedded in a circular halo of stars
Space news (February 1, 2016) – 300 million light-years away in the Bootes constellation –
Astronomers use the Hubble Tuning Fork to classify galaxies viewed during the human journey to the beginning of space and time according to their morphology. Devised by noted astronomer Edwin Hubble during the early part of the twentieth century, this galaxy classification system breaks galaxies into two general categories; elliptical and spiral galaxies.
Island universes viewed that don’t seem to fit into the two general categories of galaxies are considered irregular galaxies. Irregular galaxies have a more varied look than the general categories, often with a spiral structure that looks disturbed or disrupted. It’s this disrupted structure, and other hints, that makes astronomers think the more chaotic and varied look of these island universes could often be due to titanic collisions between galaxies.
The galaxy viewed in the image above is Mrk 820 (also LEDA 52404 or IRAS F14379+3142), a lenticular galaxy in the transition zone between the two general categories of galaxies (Type S0). Astronomers looking closer at his spectacular island universe believe it shows hints of spiral arms imprinted on a halo of stars, which is unusual for lenticular galaxies. Lenticular galaxies generally have a notable central bulge and disk, but no spiral arms.
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