Kreutz group

from Wikipedia, the free encyclopedia

The Kreutz group ( English: Kreutz Sungrazers , after the astronomer Heinrich Kreutz , who was the first to recognize the group membership) is a group of comets that come very close to the sun during their perihelion . They form a subgroup of the Sungrazer ( sun stripes or sun scratches ). The comets of the Kreutz group are believed to be fragments of a much larger comet that broke several centuries ago while orbiting the sun.

Several members of the Kreutz group developed into very bright comets that were visible next to the sun even during the day . B. Comet Ikeya-Seki , which appeared in 1965 and is considered one of the brightest comets of the last millennium.

Since the SOHO space probe went into operation in 1995, several hundred of the group's smaller comets have been discovered, some by amateur astronomers .

Discovery and historical observations

A drawing of the Great Comet of 1843, of Tasmania from

The first comet whose orbit could be determined to be very close to the Sun was the Great Comet of 1680 . It  passed the visible sun surface at a distance of only 200,000 km or 0.0013  astronomical units (AU) - this corresponds to about half the distance between the earth and the moon . Astronomers of the time, including Edmond Halley , suspected that it might be the same comet that was visible in the daytime sky in 1106. 163 years later, the Great Comet of 1843 appeared , which also passed extremely close to the Sun. The determination of its orbit showed a periodicity of several hundred years. Some astronomers saw it as the return of the comet of 1680. In 1880 a bright comet appeared, which moved in a very similar orbit as the comet of 1843. In 1882 another very conspicuous comet became visible, known as the Great September Comet .

Photograph of the Great Comet from 1882

This led some astronomers to suspect that all observations could be one and the same comet, although its orbital period must have been greatly reduced over time, e.g. B. as a result of deceleration by a denser medium near the sun.

According to another thesis, it was fragments of a larger comet. This thesis, first expressed in 1880, was substantiated when it was observed that the Great Comet of 1882 broke into several pieces after passing through the perihelion. In 1888 Heinrich Kreutz published a paper in which he stated that the comets of 1843, 1880 and 1882 could be fragments of a giant comet that had broken during previous passes. The comet of 1680 does not belong to this group, however.

Another comet, which could be assigned to the group due to its orbital properties , appeared in 1887, but the next only again in 1945. In the 1960s, two appeared in quick succession: in 1963 the comet Pereyra and in 1965 Ikeya-Seki, which shortly before the perihelion in three pieces broke. The appearance of two comets of the Kreutz group at such short intervals led to a closer study of the group's dynamics.

dynamics

A 1967 study by Brian Marsden was the first attempt to determine the body of origin of the Kreutz group. All known members of the group who were observed up to 1965 had a similar orbit inclination of about 144 ° and similar perihelion lengths of 280–282 °, with occasional deviations which, however, were due to imprecise orbit determinations. On the other hand, there were larger deviations with regard to the perihelargument and the length of the ascending node .

According to Marsden, the Kreutz group can in turn be divided into two groups, which were created as a result of multiple breakdowns of the original body:

Subgroup I.

A comparison of the orbits of Ikeya-Seki and the comet of 1882 led to the conclusion that they were fragments that were formed during the same perihelion passage of the original comet. The most likely candidate for this was the comet of 1106 . The comets of 1689, 1702 and 1945 could also belong to this "subgroup I", although their orbits could not be determined precisely enough.

Subgroup II

The orbits of the comets of 1843 and 1963 also have something in common with each other. When calculating the railways back, however, there are larger differences. These members of "Subgroup II", to which the comets of 1668, 1695, 1880 and 1963 also belong, presumably arose from several perihelion passages.

General

The division into two subgroups suggests that they descend from two different comets. However, these could in turn represent fragments of an even larger original body. A possible candidate is a comet dating from 373 BC. Was observed by Aristotle and Ephorus ( Great Comet from 373 BC ). Ephorus reports that the comet broke in two. The original comet must have been a very large specimen with an estimated diameter of 100 km (for comparison: the bright comet Hale-Bopp had a diameter of about 40 km).

So far, four times as many comets in subgroup I have been discovered as members of subgroup II. This suggests that the original comet broke into pieces of different sizes.

Although the orbit of the comet of 1680 differs quite a bit from that of the two subgroups, it is probably also assigned to the Kreutz group, although it was formed a long time ago by fragmentation.

The Kreutz group is probably not a unique phenomenon. Studies show that comets with a large inclination and perihelion distances of less than 2 AU can develop into sungrazers due to the gravitational effect of the sun. There is a 15% chance for Comet Hale-Bopp.

Current research

Due to the close distance to the sun, most of the comets of the Kreutz group are difficult to observe from Earth. Except for the very bright representatives, most of them went unnoticed in the past.

In the 1980s, two satellites destined for solar observation discovered several new members of the group. Since the SOHO space probe went into operation in 1995, it has been possible to observe comets in close proximity to the sun. Since then, several hundred Sungrazers have been discovered, around 90% of which can be attributed to the Kreutz group. Some were only a few meters in diameter. None of the Sungrazers discovered by SOHO survived the perihelion passage. Some fell directly into the sun, the rest evaporated near the sun. An exception to this rule is C / 2011 W3 (Lovejoy) , which in December 2011 was the only comet of the Kreutz group that has been observed so far, apparently largely unscathed after passing through the perihelion.

Around a third of the Sungrazers found using SOHO were discovered by amateur astronomers who evaluated the photos from the satellite on the Internet . The Briton Michael Oates found 144 comets, the German Rainer Kracht 156 comets (as of November 2005).

The SOHO observations showed that the Kreutz comets often appear in pairs with an interval of a few hours. These fragments evidently formed at a greater distance from the Sun.

The Kreutz comets should be identifiable as an independent group for thousands of years. Their orbits will probably change due to the gravitational influences of the large celestial bodies in the solar system . In the long term, the group will disintegrate through further fragmentation and evaporation near the sun.

The last bright comet of the group was the 1970 published C / 1970 K1 (White-Ortiz-Bolelli) . At the moment it is not possible to estimate when the next conspicuous Kreutz comet will appear. However, assuming that at least ten have been visible to the naked eye in the last 200 years, this is likely to happen in the not too distant future.

In fact, comet C / 2020 X3 (SOHO) , found in December 2020 and observed during the total solar eclipse on December 14, 2020 , is apparently a member of the Kreutz group.

literature

  • ME Bailey, VV Emel'yanenko, G. Hahn, NW Harris, KA Hughes and K. Muinonen: Orbital evolution of Comet 1995 O1 Hale-Bopp. In: Monthly Notices of the Royal Astronomical Society . Volume 281, 1996, pp. 916-924.
  • ME Bailey, JE Chambers and G. Hahn: Origin of sungrazers - A frequent cometary end-state. In: Astronomy and Astrophysics . Volume 257, 1992, pp. 315-322.
  • HCF Kreutz: Investigations into the comet system 1843 I, 1880 I and 1882 II. Printed by C. Schaidt, CF Mohr nachfl., Kiel 1888.
  • BG Marsden: The sungrazing comet group. In: Astronomical Journal . Volume 72, 1967, p. 1170.
  • BG Marsden: The sungrazing comet group. II. In: Astronomical Journal . Volume 98, 1989, p. 2306.
  • BG Marsden: The Sungrazing Comets Revisited. In: CI Lagerkvist, H. Rickman and BA Lindblad (eds.): Asteroids, comets, meteors III. Proceedings of meeting (AMC 89) . Universitet, Uppsala 1990, p. 393.
  • Zdenek Sekanina: Kreutz sungrazers: the ultimate case of cometary fragmentation and disintegration? In: Publications of the Astronomical Institute of the Academy of Sciences of the Czech Republic . No. 89, 2001, pp. 78-93.

Web links

Commons : Kreutz Group  - collection of images, videos and audio files

Individual evidence

  1. ↑ Comet Lovejoy NASA
  2. ↑ Spaceweather December 17, 2011
  3. ↑ after Oates
  4. ↑ after Kracht
  5. ↑ K. Battams et al. : Comet C / 2020 X3 (SOHO). MPEC 2020-Y19 , on minorplanetcenter.net from December 17, 2020. In addition:
This version was added to the list of articles worth reading on November 26, 2005 .