220325 - M94 "Croc's Eye" galaxy
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click image to enlarge
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ASTRO:
type=Spiral galaxy const=Canes Venatici mag=8.2 dist=15 M ly size=45k ly IMAGE: location=EB Driveway BrtlCls=4 moon=37% WnCr exposure=DSLR OSC: 70x240s (4.7h), ISO1600 EQUIPMENT: camera=Nikon D90 (mod) optics=ES102 w24mmEP 1.7x prjctn, F=1238mm, f/12.1 filter=Optolong L-Pro LPS mount=Celestron AVX guiding=Orion 60x240mm, ZWO ASi224MC SOFTWARE: acquisition=Stellarium, APT, PHD2, processing=DSS, PSCC, RCAstro, StarNet++, TopazDeNoiseAI, LrC |
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Most galaxies don't have rings of stars and gas -- why does M94 have two? First, spiral galaxy M94 has an inner ring of newly formed stars surrounding its nucleus, giving it not only an unusual appearance but also a strong interior glow. A leading hypothesis of its origin holds that an elongated knot of stars known as a "bar" is more oval-shaped than other barred galaxies and rotates inside M94. It seems to have generated a burst of star formation inside this inner ring. Observations have also revealed another ring, an outer ring, one that is more faint, different in color, not closed, and relatively complex. What caused this outer ring is currently unknown.
M94 spans about 45,000 light years in total, lies about 15 million light years away, and can be seen with a small telescope toward the constellation of the Hunting Dogs (Canes Venatici). M94 (also known as NGC 4736) was discovered by Pierre Méchain in 1781, and catalogued by Charles Messier two days later.
The inner ring of M94 has a diameter of 70 arcseconds (about 5,400 light-years) and an outer ring has a diameter of 600″ (about 45,000 light-years). These rings appear to form at resonance points in the disk of the galaxy. The inner ring is the site of strong star formation activity and is sometimes referred to as a starburst ring. This star formation is fueled by gas driven dynamically into the ring by the inner oval-shaped bar-like structure.
In 2008 a study was published showing that M94 had very little or no dark matter present. The study analyzed the rotation curves of the galaxy's stars and the density of hydrogen gas and found that ordinary luminous matter appeared to account for all of the galaxy's mass. This result was unusual and somewhat controversial, as current models do not indicate how a galaxy could form without a dark matter halo, or how a galaxy could lose its dark matter. However, this result has yet to be confirmed or accepted by a wide range of research groups and has not been tested against the predictions of standard galaxy formation models.
M94 spans about 45,000 light years in total, lies about 15 million light years away, and can be seen with a small telescope toward the constellation of the Hunting Dogs (Canes Venatici). M94 (also known as NGC 4736) was discovered by Pierre Méchain in 1781, and catalogued by Charles Messier two days later.
The inner ring of M94 has a diameter of 70 arcseconds (about 5,400 light-years) and an outer ring has a diameter of 600″ (about 45,000 light-years). These rings appear to form at resonance points in the disk of the galaxy. The inner ring is the site of strong star formation activity and is sometimes referred to as a starburst ring. This star formation is fueled by gas driven dynamically into the ring by the inner oval-shaped bar-like structure.
In 2008 a study was published showing that M94 had very little or no dark matter present. The study analyzed the rotation curves of the galaxy's stars and the density of hydrogen gas and found that ordinary luminous matter appeared to account for all of the galaxy's mass. This result was unusual and somewhat controversial, as current models do not indicate how a galaxy could form without a dark matter halo, or how a galaxy could lose its dark matter. However, this result has yet to be confirmed or accepted by a wide range of research groups and has not been tested against the predictions of standard galaxy formation models.