NASA が超大質量ブラック ホールの衝突サイクルを追跡

• Milky Way, likely formed larger galaxies through collisions in the early Universe.
• These newly-discovered merging dwarf galaxies can be used as analogs for more distant ones that are too faint to observe.
• The dwarf galaxies are on collision courses and are found in the galaxy clusters Abell 133 and Abell 1758S.

Evidence for two pairs of supermassive black holes in dwarf galaxies on collision courses has been found with Chandra. The two pairs are shown in X-rays from Chandra and optical light from the Canada-France-Hawaii telescope. The merger on the left is in a late stage and was given the single name of Mirabilis. The other merger is in the early stages and the two dwarf galaxies are named Elstir (bottom) and Vinteuil (top). Astronomers think that dwarf galaxies – those about 20 times less massive than the Milky Way – grow through mergers with others. This is an important process for galaxy growth in the early Universe and this discovery provides examples for scientists to study in greater detail. Credit: X-ray: NASA/CXC/Univ. of Alabama/M. Micic et al.; Optical: International Gemini Observatory/NOIRLab/NSF/AURA

A new study using NASA’s Chandra X-ray Observatory has tracked two pairs of supermassive black holes in dwarf galaxies on collision courses. This is the first evidence for such an impending encounter, providing scientists with important information about the growth of black holes in the early Universe.

By definition, dwarf galaxies contain stars with a total mass less than 3 billion Suns — or about 20 times less than the Milky Way. Astronomers have long suspected that dwarf galaxies merge, particularly in the relatively early Universe, in order to grow into the larger galaxies seen today. However, current technology cannot observe the first generation of dwarf galaxy mergers because they are extraordinarily faint at their great distances. Another tactic — looking for dwarf galaxy mergers closer by — had not been successful to date.

新しい研究では、チャンドラの深部 X 線観測の体系的な調査を実施し、それらを NASA の広赤外線サーベイ エクスプローラー (WISE) からの赤外線データおよびカナダ、フランス、ハワイの望遠鏡 (CFHT) からの光学データと比較することで、これらの課題を克服しました。

ブラックホールを取り囲む物質は何百万度にも加熱され、大量のX線を放出する可能性があるため、チャンドラはこの研究で特に価値がありました。 チームは、2 つのブラック ホールの証拠として衝突する矮小銀河の明るい X 線源のペアを探し、2 つの例を発見しました。

超大質量ブラック ホールのペアの証拠は、チャンドラとの衝突サイクルの矮小銀河で発見されています。 このペアは、チャンドラからの X 線と、カナダ-フランス-ハワイ望遠鏡からの光学光で見られます。 左の合併は後期段階であり、ミラビリスという個別の名前が付けられています。 もう一方の合体は初期段階にあり、2 つの矮小銀河は Elstir (下) と Vinteuil (上) と名付けられました。 天文学者は、天の川銀河の 20 分の 1 の矮小銀河は、他の銀河との合体によって成長すると考えています。 これは初期宇宙における銀河の成長にとって重要なプロセスであり、この発見は科学者がより詳細に研究するための例を提供します。 クレジット: X 線: NASA/CXC/Univ. アラバマ/m. ミシックら。 光学: Gemini Observatory International/NOIRLab/NSF/AURA

1 つのペアは、左の合成画像に見られる、地球から 7 億 6000 万光年に位置するアベル 133 銀河団にあります。 ピンクがチャンドラのX線データ、青がCFHTの光学データ。 この矮小銀河のペアは、合体の後期段階にあるように見え、衝突による潮汐効果によって長い尾を示しています。 新しい研究の著者は、それが絶滅の危機に瀕した後、それを Mirabilis と名付けました[{” attribute=””>species of hummingbird known for their exceptionally long tails. Only one name was chosen because the merger of two galaxies into one is almost complete. The two Chandra sources show X-rays from material around the black holes in each galaxy.

X-ray and optical composite of Mirabilis. Credit: X-ray: NASA/CXC/Univ. of Alabama/M. Micic et al.; Optical: International Gemini Observatory/NOIRLab/NSF/AURA

The other pair was discovered in Abell 1758S, a galaxy cluster about 3.2 billion light-years away. The composite image from Chandra and CFHT is on the right, using the same colors as for Mirabilis. The researchers nicknamed the merging dwarf galaxies “Elstir” and “Vinteuil,” after fictional artists from Marcel Proust’s “In Search of Lost Time”. Vinteuil is the galaxy on the top and Elstir is the galaxy on the bottom. Both have Chandra sources associated with them, again from X-rays from material around the black holes in each galaxy. The researchers think these two have been caught in the early stages of a merger, causing a bridge of stars and gas to connect the two colliding galaxies from their gravitational interaction.

X-ray and optical composite of Elstir & Vinteuil. Credit: X-ray: NASA/CXC/Univ. of Alabama/M. Micic et al.; Optical: International Gemini Observatory/NOIRLab/NSF/AURA

The details of merging black holes and dwarf galaxies may provide insight to our Milky Way’s own past. Scientists think nearly all galaxies began as dwarf or other types of small galaxies and grew over billions of years through mergers. Follow-up observations of these two systems will allow astronomers to study processes that are crucial for understanding galaxies and their black holes in the earliest stages of the Universe.

これらの調査結果を説明する論文は、最近の号に掲載されました の[{” attribute=””>Astrophysical Journal.

Reference: “Two Candidates for Dual AGN in Dwarf-Dwarf Galaxy Mergers” by Marko Mićić, Olivia J. Holmes, Brenna N. Wells and Jimmy A. Irwin, 22 February 2023, The Astrophysical Journal.
DOI: 10.3847/1538-4357/aca1bb

The authors of the study are Marko Micic, Olivia Holmes, Brenna Wells, and Jimmy Irwin, all from the University of Alabama at Tuscaloosa.

NASA’s Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.