Difference between revisions of "Spiral galaxy"
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A '''spiral galaxy''' is a [[galaxy]] consisting of a rotating disk of [[star]]s, [[gas]] and [[dust]] which has a number of arms extending outwards from the galactic centre.<ref>[https://www.britannica.com/topic/galaxy/Types-of-galaxies#ref559197 Galaxies] from britannica.com</ref> Some spiral galaxies have a prominent bulge around the centre, while others have a bar crossing the centre with the spiral arms extending from the ends of the bar. They tend to be fairly large and blue in color. | A '''spiral galaxy''' is a [[galaxy]] consisting of a rotating disk of [[star]]s, [[gas]] and [[dust]] which has a number of arms extending outwards from the galactic centre.<ref>[https://www.britannica.com/topic/galaxy/Types-of-galaxies#ref559197 Galaxies] from britannica.com</ref> Some spiral galaxies have a prominent bulge around the centre, while others have a bar crossing the centre with the spiral arms extending from the ends of the bar. They tend to be fairly large and blue in color. | ||
| − | Some Creation scientists have argued that spiral galaxies are [[Arguments for a recent creation|evidence of a young universe]].<ref>[https://answersingenesis.org/astronomy/cosmology/galaxies-unexplained-spirals/ Galaxies-unexplained spirals] from answersingenesis.org</ref> | + | Some Creation scientists have argued that spiral galaxies are [[Arguments for a recent creation|evidence of a young universe]].<ref>[https://answersingenesis.org/astronomy/cosmology/galaxies-unexplained-spirals/ Galaxies-unexplained spirals] from answersingenesis.org</ref> Specifically, the spiral arms in the galaxy should smear out after several rotations as the inner stars orbit faster than the outer stars. This is known as the "winding problem." A young universe solves the winding problem as it means there has not been enough time for galaxies to rotate even once, the Milky Way takes around 200 million years to complete a single revolution, and so not enough time for the arms to smear out.<ref>[https://phys.org/news/2015-02-milky-rotate.html Why does the Milky Way rotate?] from phys.org</ref> |
The [[Milky Way]] is a spiral galaxy, as is the [[Andromeda galaxy]], the closest large galaxy to the Milky Way. | The [[Milky Way]] is a spiral galaxy, as is the [[Andromeda galaxy]], the closest large galaxy to the Milky Way. | ||
Revision as of 14:27, September 17, 2017
A spiral galaxy is a galaxy consisting of a rotating disk of stars, gas and dust which has a number of arms extending outwards from the galactic centre.[1] Some spiral galaxies have a prominent bulge around the centre, while others have a bar crossing the centre with the spiral arms extending from the ends of the bar. They tend to be fairly large and blue in color.
Some Creation scientists have argued that spiral galaxies are evidence of a young universe.[2] Specifically, the spiral arms in the galaxy should smear out after several rotations as the inner stars orbit faster than the outer stars. This is known as the "winding problem." A young universe solves the winding problem as it means there has not been enough time for galaxies to rotate even once, the Milky Way takes around 200 million years to complete a single revolution, and so not enough time for the arms to smear out.[3]
The Milky Way is a spiral galaxy, as is the Andromeda galaxy, the closest large galaxy to the Milky Way.
Classification
Spirals are classified by whether they contain a bar and how tightly wound its arms are. If a spiral galaxy contains a bar, it is labelled "SB" and simply "S" if it has no bar.[4] The tightness of the arms is characterised by the letters a, b and c, with a meaning a galaxy with the tightest winding, c with the loosest winding and b somewhere in between. The size of the bulge decreases with this classification, with a having the largest bulge and c having the smallest.[4] For example, a barred spiral galaxy with a large bulge and tightly wound arms would be labelled "SBa".
References
- ↑ Galaxies from britannica.com
- ↑ Galaxies-unexplained spirals from answersingenesis.org
- ↑ Why does the Milky Way rotate? from phys.org
- ↑ 4.0 4.1 Galaxy classification from spacetelescope.org
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