gingadan.com

NGC 7078 (Globular Cluster, M15)


Home > Messier > NGC7078
Down
Movie

NGC 7078, M15
Globular Cluster (球状星団)
Gb IV


別名 (Other names)
GCL 120, Messier 15

明るさ (Brightness)
6.3等級

星座 (Constellation)
ペガスス座 (Peg) (Pegasus)

距離 (Distance)
35,000光年 (35,000 light-years)

M15(NGC7078)はペガスス座にある球状星団。
1746年にジャン・ドミニク・マラルディがド・シェゾー彗星(C/1746 P1)を観測中に発見した。M2 を発見した5日後であった。彼は「星雲状でかなり明るく大きな星がある」と記している。シャルル・メシエは1764年に「星のない星雲。まるく中心部が輝く」と記しており、高名なメシエの機材の方が貧弱であったことを示している。

ペガスス座の顔を形作っているθ星とε星を結んでε星の方向に伸ばした線上にある。
双眼鏡等では、すぐ隣の6等星と並んでいるぼやっとした光芒がわかるので比較的探しやすい。

M15 は変光星を多く含む球状星団として知られている。ケンタウルス座のω星団とりょうけん座の M3 に次ぐ変光星の多さ。年々視直径が増大していることも観察されている。また、M15 の中には球状星団で初めて惑星状星雲が見つかっている。現在観察されている球状星団の中で最も密集度の高い球状星団。

通常、球状星団や銀河などの恒星系は中心に向かって密度が大きくなっており、最も中心近くには密度一定のコアと呼ばれる領域があるが、M15は中心付近に密度一定のコアが見られず、中心が「尖った」密度分布を持っている。このような球状星団は他にもいくつか見つかっており、post core-collapsed cluster と呼ばれている。
一般に自己重力でまとまっている系は時間とともに中心密度が際限なく上昇していくことが分かっており、このような過程は重力熱力学的カタストロフィーと呼ばれる。
M15 はこのような物理過程が実際に起こっていると考えられる実例である。また、M15 の中心部はこのような高い密度を持っており、また1974年に中心部からX線が放射されていることが観測されていることから、中心には銀河中心と同様の大質量ブラックホールがあるのではないかと考える研究者もいる。
そのため、M15 の中心核はしばしばハッブル宇宙望遠鏡などを用いた観測の対象となっている。

M13と同様に、M15には多くの赤色巨星が含まれている。星団は非対象の楕円形をしており、周囲にはクモの脚と言われるような星の流れがある。内部には斑点のような2つの暗い部分がある。
星団の北東には1928年にピーズによって発見されたピーズ1と呼ばれる惑星状星雲がある。
球状星団内部に惑星状星雲が発見されているのは、M22とM15のみである。
M22にある惑星状星雲は10"×7"ほどの大きさに見えるが、ピーズ1は1"ほどの大きさにしか見えない。

双眼鏡ではぼんやりとまるい星雲状に見える。口径8cmの望遠鏡で周囲の星がわずかに見え始める。
10cmで次第にはっきりと周辺の星が分かれてくる。しかし、熟練者の記録でも10cmでも困難だとする記録があり、空の条件に依存する。

NGC 7078 (M15) is a globular cluster located 35,000 light years from the Earth in the constellation Pegasus.

NGC 7078 (Globular Cluster, M15) : Picture

Globular Cluster M15
Globular Cluster M15 from Hubble
(C) ESA, Hubble, NASA
Stars, like bees, swarm around the center of bright globular cluster M15. This ball of over 100,000 stars is a relic from the early years of our Galaxy, and continues to orbit the Milky Way's center. M15, one of about 170 globular clusters remaining, is noted for being easily visible with only binoculars, having at its center one of the densest concentrations of stars known, and containing a high abundance of variable stars and pulsars. Released only recently, this sharp image taken by the Earth-orbiting Hubble Space Telescope spans about 120 light years. It shows the dramatic increase in density of stars toward the cluster's center. M15 lies about 35,000 light years away toward the constellation of Pegasus.

Comet Garradd and Messier 15
Comet Garradd and Messier 15
(C) Gregg Ruppel
Recorded on August 2, this telescopic composite image catches Comet Garradd (C/2009 P1) in the same field of view as globular star cluster M15. The celestial scene would have been a rewarding one for influential 18th century comet hunter Charles Messier. While Messier scanned French skies for comets, he carefully cataloged positions of things which might be fuzzy and comet-like in appearance but did not move against the background stars and so were definitely not comets. M15 (lower right), the 15th entry in his famous not-a-comet catalog, is now understood to be a cluster of over 100,000 stars some 35,000 light-years distant. The comet, discovered in August 2009 by astronomer G. J. Garradd (Siding Spring Observatory, Australia) is currently sweeping across the constellation Pegasus, some 13 light-minutes from Earth. Shining faintly around 9th magnitude, comet Garradd will brighten in the coming months, predicted to be just below naked eye visibility near its peak in February 2012.

Globular Cluster M15
Globular Cluster M15 from Hubble
(C) ESA, Hubble, NASA

Globular Cluster M15
Globular Cluster M15
(C) Haldan Cohn (Indiana U.) et al., WIYN, NOAO, NSF

X-Ray Stars in M15
X-Ray Stars in M15
(C) N. White and L. Angelini (LHEA), GSFC, CXO, NASA (Inset: Hubble Heritage Team)
Side by side, two x-ray stars greeted astronomers in this false-color Chandra Observatory x-ray image of a region near the core of globular star cluster M15. The greeting was a pleasant surprise, as all previous x-ray images of the cluster showed only one such source where Chandra's sharper x-ray vision now reveals two. These x-ray sources are modeled as neutron star binary systems. Each is a city-sized neutron star in close orbit with a normal stellar companion. X-rays are generated as matter from the normal star falls onto the compact neutron star. This break through explains why observations of the previously recognized lone neutron star binary system in M15 were difficult to reconcile with any single model. It also suggests that other globular star clusters which roam the halo of our Milky Way galaxy and seem to contain only one such neutron star x-ray source may in fact contain more. An optical Hubble Space Telescope image of the dense M15 cluster is inset at the upper right.

M15: Dense Globular Star Cluster
M15: Dense Globular Star Cluster
(C) H. Bond et al., Hubble Heritage Team (STScI / AURA), NASA
Life might get dull at the core of M15 but the sky would always be bright with stars! In fact, only 40,000 light-years away in the constellation Pegasus, M15 is one of the most densely packed globular star clusters in our Milky Way Galaxy. This stunning Hubble Space Telescope image of M15 shows thousands of individual stars across the central 10 or so light-years of the cluster, also cataloged as NGC 7078. Yet even the Hubble's sharp vision can't clearly separate the stars at this cluster's core. Globular star clusters harbor from a hundred thousand up to a million stars and roam the Milky Way halo. Like most globulars, M15 is filled with ancient stars, about 12 billion years old compared to the Sun's estimated 4.5 billion years. Its cool red giant stars appear yellowish in this color composite image. Unlike most globulars, M15 displays a planetary nebula, the briefly visible gaseous shroud of a dying star. Can you pick it out? Cataloged as Kuestner 648, M15's planetary nebula is the round pinkish cloud at the upper left.

At The Core Of M15
At The Core Of M15
(C) P. Guhathakurta (UCO/Lick, UC Santa Cruz), NASA

Globular Cluster M15 Globular Cluster M15
Globular Cluster M15 from Hubble
(C) ESA, Hubble, NASA
Globular Cluster M15 from Hubble
(C) ESA, Hubble, NASA
Globular Cluster M15 Globular Cluster M15
Globular Cluster M15
(C) Haldan Cohn et al., WIYN, NOAO, NSF
M15: Dense Globular Star Cluster
(C) H. Bond et al., NASA
Up
Up

NGC 7078 (Globular Cluster, M15) : Movie

Hubblecast 69: What has Hubble learned from star clusters?
The NASA/ESA Hubble Space Telescope has observed many star clusters. As well as being scientifically interesting, these clusters produce stunning images, appearing like sparkling baubles in the sky.

This episode of the Hubblecast looks at how Hubble has studied and imaged these beautiful objects, also introducing a striking new image of Messier 15, one of the oldest globular clusters in our skies. This is the best ever image of this cluster, which contains over 100,000 stars, a planetary nebula known as Pease 1 (otherwise named PN Ku 648 or Kürster 648), and something more exotic: at its core, it is thought to host a rare type of black hole.
Up
Home > Messier > NGC7078
Up

「ウィキペディア(wikipedia):フリー百科事典」より文章引用。
M15 (天体). (2013, November 26). In Wikipedia.
gingadan.com ブログパーツ