SN 1994I is a

Type Ic supernova Type Ib and Type Ic supernovae are categories of supernovae that are caused by the stellar core collapse of massive stars. These stars have shed or been stripped of their outer envelope of hydrogen, and, when compared to the spectrum ...

discovered on April 2, 1994 in the

Whirlpool Galaxy The Whirlpool Galaxy, also known as Messier 51a, M51a, and NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classifie ...

amateur astronomer Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomers m ...

s Tim Puckett and Jerry Armstrong of the Atlanta Astronomy Club. Type Ic supernova are a rare type of

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

that result from the explosion of a very

massive star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

that has shed its outer layers of

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

and

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

. The explosion results in a highly luminous burst of radiation that then dims over the course of weeks or months. SN 1994I was a relatively nearby supernova, and provided an important addition to the then small collection of known Type Ic supernova. Very early images were captured of SN 1994I, as two high school students in Oil City,

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

serendipitously took images of the Whirlpool Galaxy using the 30-inch telescope at

Leuschner Observatory Leuschner Observatory, originally called the Students' Observatory, is an observatory jointly operated by the University of California, Berkeley and San Francisco State University. The observatory was built in 1886 on the Berkeley campus. For many ...

on March 31, 1994, which included SN 1994I just after it began to brighten.

Discovery and observations

SN 1994I was independently discovered by multiple observers, with the first reports from amateur astronomers Tim Puckett and Jerry Armstrong, followed within the hour by reports by amateurs Wayne Johnson and Doug Millar, Richard Berry, and Reiki Kushida. It was confirmed quickly by Michael Richmond and

Alex Filippenko Alexei Vladimir "Alex" Filippenko (; born July 25, 1958) is an American astrophysicist and professor of astronomy at the University of California, Berkeley. Filippenko graduated from Dos Pueblos High School in Goleta, California. He received a Ba ...

using the Berkeley Automated Imaging Telescope at Leuschner Observatory, who noted that SN 1994I was particularly blue. Initial reports disagreed on the nature of the supernova, with different teams claiming that it was a

Type Ia supernova A Type Ia supernova (read: "type one-A") is a type of supernova that occurs in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white ...

, a

Type II supernova A Type II supernova (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun () to undergo this ...

, and a Type Ic supernova. Supernova types are observationally distinguished by the presence or absence of

spectral line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

s, with

being the most important diagnostic. After a week of more data being collected, consensus grew among observers that SN 1994I was a Type Ic. By chance, observations of SN 1994I were obtained before its discovery was reported. High school students Heather Tartara and Melody Spence requested observations of the Whirlpool Galaxy on March 29 and 31, 1994. Their request was made through the Hands-On Universe program, which allows elementary and high school students to request observations on automated telescopes. Their images captured the Whirlpool Galaxy just before and after SN 1994I began to brighten, and are some of the earliest data recorded for a supernova.

Characteristics

The progenitors of Type Ib, Ic, and II supernovae are commonly called core-collapse supernovae, as they result from massive stars that cannot produce enough

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

to balance the inward force of self-

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

. Yet all Type I supernova are distinguished by their lack of hydrogen

absorption line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

s, and Type Ic also lack

lines. Initial failure to detect hydrogen or helium led to SN 1994I being classified as a Type Ic. Follow-up observations showed very weak helium absorption features, and thus SN 1994I seems to bridge the two classes, though it is still considered one of the best examples of a Type Ic supernova. There are two proposed mechanisms for removing the hydrogen. One suggests that the progenitors of Type Ib and Ic may be Wolf-Rayet stars, as they produce

stellar wind A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. D ...

s that could blow away the hydrogen. The other possibility is mass transfer to a

companion star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

. The proximity of SN 1994I allowed for detailed comparison of models to the observations. These comparisons showed that SN 1994I was consistent with having lost its outer layers to a companion.

References

External links

Light curves and spectra
on th
Open Supernova Catalog
{{DEFAULTSORT:SN 1994I Supernovae 19940402 Canes Venatici