一顆超年輕在銀河系內的超新星爆發

Astrosing

　這是一顆超年輕在銀河系內的超新星爆發

(摘自:中國時報 2008.05.16　
140歲 銀河超新星超年輕
潘勛／綜合華盛頓十四日外電報導)
http://chandra.harvard.edu/
http://www.nasa.gov/mission_pages/chandra/news/08-062.html

美、英兩國的天文學家小組14日表示，已發現地球身處的銀河系裡最近形成的超新星，距今約140年，此一發現有助於增長人類的知識，了解星系的大爆炸與銀河系的運作方式。

    　這顆超新星代號「G1.9+0.3」，位於射手座，是由射電（無線電波）及X射線兩種天文望遠鏡觀測到的，比前一顆銀河系超新星「仙后座A」（約爆發於1680年）要年輕約200歲。因為它位處銀河系中心，當地有氣體及太空塵組成緻密場域，所以最初發生耀眼爆炸時，並沒被觀測到。

    　這項研究係由北卡羅萊納州立大學專家雷諾茲帶頭進行。雷諾茲表示，20多年前天文學家首度發現這顆超級新星，但估計其原始爆炸發生在400到1000年間。

    　但是，經比對「美國國家航空暨太空總署」所屬「仙陀螺」X射線望遠鏡2007年拍攝到的影像與1985年「國立射電天文台」之「極大陣列」望遠鏡所拍影像後，發現22年間，「G1.9+0.3」的殘餘物質擴張約16%，顯示其星齡比原先認定要年輕得多。超新星的星齡是依其殘餘物質的擴張速率來估定，擴張得愈快就愈年輕。

    　天文學家表示，2008年初，極大陣列望遠鏡進行多次測量，證實「G1.9+0.3」的年齡為140歲；假如其擴張減緩，那麼年齡可能還更小。因此，「G1.9+0.3」為人類有紀錄以來，地球所處銀河系中最年輕的超新星。

    　雷諾茲表示，人類使用光學望遠鏡，可以看到半個宇宙發生一些超新星爆炸，但是，如果爆炸發生在黝暗地帶，即使是在地球銀河系的「自家後院」，也會錯過，而觀測不到。

    　雷諾茲表示，「G1.9+0.3」的殘餘物質非常明亮，天文學家應該可以更犀利地透視此一奇觀，另了解它對周遭銀河系的影響。

    　大質量恆星「臨死亡」坍塌時的劇烈爆炸即為超新星，是最激烈的天體物理現象，而天文學界認為，超新星爆發過程噴射出的大量物質瀰漫在星系之間，成為孕育新一代恆星及周圍行星的原始材料。

moomi

Dear Astrosing,

學會資訊內的最新消息版是用於發放HKAS消息, 此題放在天文資訊版較適合.
所以搬到天文資訊版.

moomi

Astrosing

Dear Moomi,

  真不好意思.新手上路.請見諒.我也很關心四川的災民.

聲上

philipchung

After reading the article about the recent discovery of the "youngest" supernova in the Milky Way, I have some observations.   My observations are somewhat "educational" inclined rather than focus on the cold astronomical facts.

Key astronomical knowledge that could be learned from the news:
(1) use of the radio x-ray frequency of EM wave to probe objects obscured by dense dust and gas etc. in space;
(2) use of the rate of expanding gas cloud of the SN remnant to estimate the age of the SN explosion; TAG may wish to study the theory behind which is not too difficult.

Questions:
(1) what are the importance of this discovery?  The three points reported by 中國時報 (see first paragraph, last sentence, viz,  增長人類知識, 了解星系大爆炸, 了解銀河系的運作方式) are obviously not satisfactory since the first point is always correct but does not mean it is important.  I do not understand the meaning of the 2nd point which I think is totally irrelevant.  The 3rd point is too high-sounding and a bit abstract.   So what are the importance of this discovery from the standpoint of Astronomy which made NASA announced the news in such a high profile?  Simply becasue it is the "youngest" SN or because the discovery of Milky Way SN is not easy (~3 events per century and in fact we found none since 1680) or both or what else?

(2) The location of this G1.9+0.3 SN is very close to the centre of the Milky Way, i.e. about 30,000 light year from us, how comes an explosion occurred 140 years ago can be seen by us?  We should see the explosion only after 30,000 years from now?

I personally have my own explanations on questions (1) and (2).  But I would rather prefer hearing our fellow amateurs' views on this discovery.

mca

Before the Chinese translation was released here, I posted the original English news announced ny NASA
http://forum-test.hkas.org.hk/vi ... amp;extra=page%3D1.

For Question 1 raised by Philip Chung , it is clearly a mismatch of the English-Chinese translations in which the original news says " ... This result, obtained by NASA's Chandra X-ray Observatory and the National Radio Astronomy Observatory's Very Large Array, will help improve our understanding of how often supernovas explode in the Milky Way galaxy...”

However  中國時報 turns  the NASA original into
" 增長人類知識，了解星系大爆炸，了解銀河系的運作方式 ".

For Question 2, the ambiguity also comes from the translation.

The original news says  
"... This comparison of data pinpoints the age of the remnant at 140 years ...".   Yet the translation becomes
" ... 已發現地球身處的銀河系裡最近形成的超新星，距今約140 年 ..."

To my knowledge, there is a big difference of meaning between “age of the remnant at 140 years” and “最近形成的超新星，距今約140 年”. The age of remnant can be determined by the outmost diameter of the gaseous remnant (which is known through observation) divided by the speed of gas expansion (which can be estimated from the astrophysics model of supernova Type 1A, or from other hints that I (being amateur) don’t learnt but known to the research professionals.

My 2 cents.
Alan Chu

mca

"The age of remnant can be determined by the outmost diameter "

This should be "The age of remnant can be determined by the outmost radius"

Sorry for my  typing error.

AC

mca

More informations of the  "G1.9+0.3" supernova in Chandra webage
http://chandra.harvard.edu/press/08_releases/press_051408.html

mca

Supplement to # 5



***** The News on Supernova Remnant (SNR) G1.9+0.3  *****

I try to understand it as follows.  

1.     The expansion velocity of the SNR, in km/s, was determined by Doppler shift measurements using the VLA radio telescope.

2.     The angular size of the SNR, in arcseconds, was also known from the composite images generated by the VLA and Chandra (X-ray telescope). See the illustrations and animations in http://chandra.harvard.edu/photo/2008/g19/more.html

Both 1 and 2 are supposed not linear, i.e. the expansion rate varies as  time goes by.

3.      From 1 and 2, the supernova distance was deduced. The news has already said  G1.9+0.3 is near the Galactic center (roughly 30,000 light years away from the Sun).

4.        All supernovae are exceptionally luminous during explosion and  hardly escape from observatory detection. If our optical telescopes failed to see an expected supernova in our Galaxy, it is likely hidden in dense gas and dust clouds along the Galactic plane. The VLT and Chandra telescopes have proven so by the event of G1.9+0.3.

5.        The hints on 1 to 4 also imply that the SNR is young, meaning the observed remnant formed 140 years after the supernova explosion.

The above is purely my guess as an outsider. Could be subjective. The best is to read the official AJ Letters when available.

AC