Stephans Quintett

Aufnahme des James-Webb-Weltraumteleskops
Aufnahme des Hubble-Weltraumteleskops.

Stephans Quintett ist eine Gruppe von fünf Galaxien im Sternbild Pegasus, die am 22. September 1877[1] von dem französischen Astronom Édouard Jean-Marie Stephan entdeckt wurde. Die Galaxiengruppe besteht aus den Galaxien NGC 7317, NGC 7318A, NGC 7318B, NGC 7319 und NGC 7320C.

Beschreibung

Illustration von Stephans Quintett mit Beschriftungen
Illustration von Stephans Quintett mit Beschriftungen

Die Galaxien NGC 7317 bis NGC 7319 bilden ein räumlich enges, wechselwirkendes System in etwa 300 Millionen Lichtjahren Entfernung. Aufgrund der gegenseitigen Gravitationswirkung sind die Spiralarme der Galaxien unregelmäßig verformt.

NGC 7320 wurde ursprünglich vom Namensgeber zu Stephans Quintett gerechnet, jedoch handelt es sich bei dieser Galaxie aufgrund einer deutlich niedrigeren heliozentrischen radialen Relativgeschwindigkeit (~ 800 km/s gegenüber ~ 6500–7000 km/s bei den anderen Galaxien) um eine Vordergrundgalaxie in rund 45 Millionen Lichtjahren Entfernung, die lediglich durch die Projektion mit Stephans Quintett zusammenfällt. Stattdessen wird heute NGC 7320C zum Quintett hinzugezählt, so dass es weiterhin fünf Galaxien sind.

Wasserstoff

Anfang 2006 entdeckten Philip N. Appleton, Cong Kevin Xu (徐聪) und andere bei einer Auswertung von Aufnahmen des Spitzer-Weltraumteleskops starke Spuren von molekularem Wasserstoff (H2), der sich mit einer Geschwindigkeit von 870 km/s verteilt. Man geht davon aus, dass sich die Wasserstoffmoleküle durch die Stoßwelle bilden, die die Galaxie NGC 7318B bei ihrem Sturz ins Zentrum der Gruppe im intergalaktischen Medium auslöst.[2] Die intergalaktische Stoßwelle erstreckt sich über eine Breite von 24 kpc.[3]

Appleton, Xu und ihre Kollegen befassten sich im Laufe der folgenden Jahre intensiv mit dem Wasserstoff in Stephans Quintett.[4] Als Spitzer, ein Infrarotteleskop, am 30. Januar 2020 abgeschaltet wurde, wechselten sie zum Radioteleskop FAST in Guizhou, das mit seiner effektiven Apertur von 300 m sehr empfindlich ist. Mit seinen 19 L-Band-Detektoren beobachteten sie Stephans Quintett im Bereich der HI-Linie (21 cm). Dabei entdeckten sie eine 600 kpc große Struktur aus atomarem Wasserstoff (H1). Die Wissenschaftler nehmen an, dass sich die Struktur vor etwa 1 Milliarde Jahren durch Gezeitenkräfte gebildet hatte, die beim ersten Zusammentreffen der Galaxien von Stephans Quintett aufgetreten waren. Das Wasserstoffgas besitzt nur eine geringe Dichte (1018/cm2). Nach den geltenden Vorstellungen hätte es in dieser Form nicht über eine derart lange Zeit überdauern dürfen. Daher müssen nun neue Modelle für derartige Galaxiengruppen ausgearbeitet werden.[5][6]

Beobachtbarkeit

Die Galaxien von Stephans Quintett besitzen eine Helligkeit von etwa 13 mag. Um sie zu beobachten, benötigt man ein Teleskop mit mindestens 20 cm Öffnung.

Siehe auch

Literatur

  • C. Kevin Xu: Stephan's Quintet: A Multi-galaxy Collision. (PDF) – Zusammenfassung des Wissensstandes über Stephans Quintett, Stand Dezember 2005.
  • König, Michael & Binnewies, Stefan (2019): Bildatlas der Galaxien: Die Astrophysik hinter den Astrofotografien, Stuttgart: Kosmos, S. 401

Weblinks

Commons: Stephans Quintett – Sammlung von Bildern, Videos und Audiodateien

Einzelnachweise

  1. Tammy Plotner, Jeff Barbour: What's Up 2006 – 365 Days of Skywatching. S. 274, ISBN 978-1-4116-8287-0. (englisch), abgefragt am 29. Juni 2011.
  2. Überschallknall im All. Max-Planck-Gesellschaft zur Förderung der Wissenschaften, 3. März 2006, abgerufen am 22. Oktober 2022.
  3. Philip N. Appleton, Cong Kevin Xu et al.: Powerful High-Velocity Dispersion Molecular Hydrogen Associated with an Intergalactic Shock Wave in Stephan's Quintet. In: The Astrophysical Journal. Band 639, Nr. 2, März 2006, S. L51–L54, doi:10.1086/502646, arxiv:astro-ph/0602554 (englisch).
  4. Philip N. Appleton, Cong Kevin Xu et al.: Powerful H2 Line Cooling in Stephan's Quintet II. Group-wide Gas and Shock Modeling of the Warm H2 and a Comparison with [CII]157.7um Emission and Kinematics. In: Astrophysics of Galaxies. 17. Januar 2017, arxiv:1701.03226 (englisch).
  5. Philip N. Appleton, Cong Kevin Xu et al.: A 0.6 Mpc H i structure associated with Stephan’s Quintet. In: Nature. Band 610, Nr. 7932, 19. Oktober 2022, S. 461–466, doi:10.1038/s41586-022-05206-x, PMID 36261547, PMC 9581777 (freier Volltext) – (englisch).
  6. FAST Discovers Largest Atomic Gas Structure Around a Galaxy Group. In: nao.cas.cn. 21. Oktober 2022, abgerufen am 22. November 2022 (englisch).

Auf dieser Seite verwendete Medien

Stephan's Quintet taken by James Webb Space Telescope.jpg
An enormous mosaic of Stephan’s Quintet is the largest image to date from NASA’s James Webb Space Telescope, covering about one-fifth of the Moon’s diameter. It contains over 150 million pixels and is constructed from almost 1,000 separate image files. The visual grouping of five galaxies was captured by Webb’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI).

With its powerful, infrared vision and extremely high spatial resolution, Webb shows never-before-seen details in this galaxy group. Sparkling clusters of millions of young stars and starburst regions of fresh star birth grace the image. Sweeping tails of gas, dust and stars are being pulled from several of the galaxies due to gravitational interactions. Most dramatically, Webb’s MIRI instrument captures huge shock waves as one of the galaxies, NGC 7318B, smashes through the cluster. These regions surrounding the central pair of galaxies are shown in the colors red and gold.

This composite NIRCam-MIRI image uses two of the three MIRI filters to best show and differentiate the hot dust and structure within the galaxy. MIRI sees a distinct difference in color between the dust in the galaxies versus the shock waves between the interacting galaxies. The image processing specialists at the Space Telescope Science Institute in Baltimore opted to highlight that difference by giving MIRI data the distinct yellow and orange colors, in contrast to the blue and white colors assigned to stars at NIRCam’s wavelengths.

Together, the five galaxies of Stephan’s Quintet are also known as the Hickson Compact Group 92 (HCG 92). Although called a “quintet,” only four of the galaxies are truly close together and caught up in a cosmic dance. The fifth and leftmost galaxy, called NGC 7320, is well in the foreground compared with the other four. NGC 7320 resides 40 million light-years from Earth, while the other four galaxies (NGC 7317, NGC 7318A, NGC 7318B, and NGC 7319) are about 290 million light-years away. This is still fairly close in cosmic terms, compared with more distant galaxies billions of light-years away. Studying these relatively nearby galaxies helps scientists better understand structures seen in a much more distant universe.

This proximity provides astronomers a ringside seat for witnessing the merging of and interactions between galaxies that are so crucial to all of galaxy evolution. Rarely do scientists see in so much exquisite detail how interacting galaxies trigger star formation in each other, and how the gas in these galaxies is being disturbed. Stephan’s Quintet is a fantastic “laboratory” for studying these processes fundamental to all galaxies.

Tight groups like this may have been more common in the early universe when their superheated, infalling material may have fueled very energetic black holes called quasars. Even today, the topmost galaxy in the group – NGC 7319 – harbors an active galactic nucleus, a supermassive black hole that is actively accreting material.

In NGC 7320, the leftmost and closest galaxy in the visual grouping, NIRCam was remarkably able to resolve individual stars and even the galaxy’s bright core. Old, dying stars that are producing dust clearly stand out as red points with NIRCam.

The new information from Webb provides invaluable insights into how galactic interactions may have driven galaxy evolution in the early universe.

As a bonus, NIRCam and MIRI revealed a vast sea of many thousands of distant background galaxies reminiscent of Hubble’s Deep Fields.
Stephan's Quintet Hubble 2009.full.jpg
Galactic Wreckage in Stephan's Quintet

A clash among members of a famous galaxy quintet reveals an assortment of stars across a wide color range, from young, blue stars to aging, red stars.

This portrait of Stephan's Quintet, also known as Hickson Compact Group 92, was taken by the new Wide Field Camera 3 (WFC3) aboard NASA's Hubble Space Telescope. Stephan's Quintet, as the name implies, is a group of five galaxies. The name, however, is a bit of a misnomer. Studies have shown that group member NGC 7320, at upper left, is actually a foreground galaxy about seven times closer to Earth than the rest of the group.

Three of the galaxies have distorted shapes, elongated spiral arms, and long, gaseous tidal tails containing myriad star clusters, proof of their close encounters. These interactions have sparked a frenzy of star birth in the central pair of galaxies. This drama is being played out against a rich backdrop of faraway galaxies.

The image, taken in visible and near-infrared light, showcases WFC3's broad wavelength range.

The colors trace the ages of the stellar populations, showing that star birth occurred at different epochs, stretching over hundreds of millions of years. The camera's infrared vision also peers through curtains of dust to see groupings of stars that cannot be seen in visible light.

NGC 7319, at top right, is a barred spiral with distinct spiral arms that follow nearly 180 degrees back to the bar. The blue specks in the spiral arm at the top of NGC 7319 and the red dots just above and to the right of the core are clusters of many thousands of stars. Most of the quintet is too far away even for Hubble to resolve individual stars.

Continuing clockwise, the next galaxy appears to have two cores, but it is actually two galaxies, NGC 7318A and NGC 7318B. Encircling the galaxies are young, bright blue star clusters and pinkish clouds of glowing hydrogen where infant stars are being born. These stars are less than 10 million years old and have not yet blown away their natal cloud. Far away from the galaxies, at right, is a patch of intergalactic space where many star clusters are forming.

NGC 7317, at bottom left, is a normal-looking elliptical galaxy that is less affected by the interactions.

Sharply contrasting with these galaxies is the dwarf galaxy NGC 7320 at upper left. Bursts of star formation are occurring in the galaxy's disk, as seen by the blue and pink dots. In this galaxy, Hubble can resolve individual stars, evidence that NGC 7320 is closer to Earth.

NGC 7320 is 40 million light-years from Earth. The other members of the quintet reside 290 million light-years away in the constellation Pegasus.

These farther members are markedly redder than the foreground galaxy, suggesting that older stars reside in their cores. The stars' light also may be further reddened by dust stirred up in the encounters.

Spied by Edouard M. Stephan in 1877, Stephan's Quintet is the first compact group ever discovered.

WFC3 observed the quintet in July and August 2009. The composite image was made by using filters that isolate light from the blue, green, and infrared portions of the spectrum, as well as emission from ionized hydrogen.

These Hubble observations are part of the Hubble Servicing Mission 4 Early Release Observations. NASA astronauts installed the WFC3 camera during a servicing mission in May to upgrade and repair the 19-year-old Hubble telescope.
StephansQuintettIlustrated2.gif
Stephan's Quintet, NGC7317, NGC7318A, NGC7318B, NGC7319, NGC7320, NGC 7320C
Stephans qintett aufsuchkarte.jpg
Autor/Urheber:

Mschcsc 17:43, 12. Apr. 2007 (CEST)

, Lizenz: Bild-frei

Aufsuchkarte zu NGC7331 und Stephans Quintett

Stephan-Legend.jpg
Autor/Urheber:

Mschcsc 17:52, 12. Apr. 2007 (CEST)

, Lizenz:

Amateuraufnahme von NGC 7331 und Stephans Quintett. Aufnahme mit einem 20cm Schmidt-Cassegrain-Teleskop und einer digitalen Spiegelreflexkamera.