The Milky Way's central black hole may not be able to hide for much longer. Observations have been made three times closer to the centre of our galaxy than ever before, strengthening the case that a supermassive black hole lurks there.

The Milky Way's centre hosts a bright object called SgrA*, which may be a disc of swirling gas and dust surrounding a heavyweight black hole.

Measuring the size and shape of SgrA* could help confirm the existence of the black hole. But a blur of clouds between the galactic centre and the Earth has prevented astronomers from getting a clear view of the object's shape.

Now, a team has managed to get three times closer than previous studies in viewing SgrA*. They did it by looking for the object's higher frequency radio signals, which cut through intervening gas and dust.

Linked telescopes

The size of SgrA* suggests the matter it contains is about 10 times denser than previous measurements, bolstering the idea that the object harbours a black hole, says astronomer Sheperd Doeleman of MIT's Haystack Observatory: "Our results are more evidence that we are looking at a black hole."

To image SgrA*, Doeleman and colleagues linked radio telescopes in Hawaii, Arizona, and California to create a telescope that was effectively 4500 kilometres wide. They used it to zoom in on the bright centre of the Milky Way with a resolution 1000 times that of Hubble Space Telescope.

So far, the team cannot produce dramatic pictures of SgrA*. But Doeleman says the technique could allow astronomers to clearly discern the shape of the disc within three to five years.

That's because future radio telescopes, such as Chile's Atacama Large Millimetre Array, due to become operational in 2010, will allow astronomers to use even shorter wavelengths to pierce through the galaxy's dust.

Black hole shadow

The images could reveal whether SgrA* has a 'shadow', a region in its centre where light is dimmed and reddened because it is pulled towards the black hole.

If SgrA* is indeed a disc of material swirling into the black hole, future observations could reveal how it is aligned.

Astronomers expect it may not spin in the plane of the Milky Way, since that would hint that the black hole at the disc's centre is actually the result of the merger of two galaxies. After the galaxies merged, their central black holes would have united as well, and the galaxy's gravity might not have had enough time to pull the disc around them into alignment with the galactic disc.

Further observations could measure elusive features, like the black hole's spin, by tracking the progress of flares of radiation – created when matter collides with the black hole – that whip around as the black hole spins.

galaxy

n.

1. 【天】銀河

2. 一群(尤指出色的人或燦爛的事物)


lurk

vi.[Q]

1. 潛伏,埋伏

a man lurking in the shadows

潛伏在幽暗處的人

2. (危險等)潛在

3. 偷偷地行動

swirl

vi.

1. 打旋,旋轉[Q]

2. 捲曲,盤繞[Q]

3. 暈眩,昏亂

vt.

1. 使打旋;使捲曲[O]

n.[C]

1. 打旋,旋轉

2. 渦流;漩渦;拳曲狀物[(+of)]

3. 暈眩,昏亂

4. 紛亂

galactic

a.

1. 乳汁的

2. 【天】銀河的

intervening

a.

1. 介於中間的;發生於其間的

bolster

n.[C]

1. 長枕;墊枕;靠枕

2. 墊子;襯墊

3. 支持物;承板;承材

vt.

1. 支撐;加固;援助;支持[(+up)]

discern

vt.[W]

1. 分辨,識別;看出,察覺到[+that][+wh-]

He discerned her plan immediately.

他一下子就看出她的打算。

He was just able to discern the road in the dark.

黑暗中,他僅能勉強把路辨清。

2. 認識,領悟

vi.

1. 辨明,分清[W]

dim
a.

1. 微暗的;暗淡的

2. 模糊的,朦朧的

3. (眼睛)模糊的,看不清楚的

4. 【口】頭腦遲鈍的

5. 悲觀的,懷疑的

vt.

1. 使變暗淡;使變模糊

vi.

1. 變暗淡;變模糊


redden
vt.

1. 使變紅,染紅

vi.

1. 變紅;臉紅

I saw him redden with pleasure.

我看到他高興得臉都紅了。

elusive
a.

1. 逃避的,躲避的

2. 難以理解的,難以記起的

He remained as elusive as ever.

他還是那樣令人難以捉摸。

flare(flares
喇叭褲)
vi.

1. (火焰)閃耀;(搖曳不定地)燃燒;閃亮[(+up/out)]

2. (女裙等)呈喇叭形展開

3. (船舷)外傾

4. 突然發怒(或激動)[(+at)]

vt.

1. 使閃亮,使閃閃地燃燒

2. 用發光信號發出

3. 使(女裙等)呈喇叭形展開

4. 使(船舷)外傾

n.[C]

1. (瞬間的)閃耀的火光;搖曳的火焰[S]

2. 閃光信號,照明彈;照明燈

3. (怒氣等的)爆發

4. (衣裙等的)呈喇叭形展開(或展開部分)

5. (太陽的)耀斑

radiation
n.

1. 發光;發熱;輻射[U]

2. 輻射能;放射線,放射物[C][U]

3. 發射;傳播[U]

4. 【生】輻射形進化[U]

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