11年來最強神秘訊號!它們到底是「何方神聖」?

lifeknowledge     2018-03-22     檢舉

天文學家偵測到有史以來最強最亮的快速電波爆發(FRB),其「訊噪比」較目前紀錄保持者還要高出 4 倍有餘,極其驚人,只是天文學家還是不知道這些電波起源為何,神秘面紗仍未掀開。

快速電波爆發(fast radio burst,縮寫 FRB)是來自太空未知區域的毫秒無線電波突發,從 2007 年首次記錄至今已逾 10 年,這些奇怪訊號非常明亮,於空中一閃而過卻可能帶來相當數億個太陽的能量,天文學家始終不知它們是何方神聖,可能是宇宙巨大災難事件的產物,也可能是科幻最愛的外星文明。

迄今為止,我們已有 33 次快速電波爆發的記錄,但除了最神秘的「FRB 121102」一直重複出現外,其餘均是一次性事件,無法繼續追溯來源,也因此 FRBs 仍是宇宙一大謎團,多數科學家懷疑它們是由黑洞或中子星碰撞等巨大災難事件產生。

今年 3 月上旬,澳洲帕克斯天文臺(Parkes Observatory)的無線電望遠鏡連續紀錄到 3 個新訊號,分別為 3 月 1 日的「FRB 180301」、9 日的「FRB 180309」以及 11 日的「FRB 180311」,其中「FRB 180309」更是有史以來檢測到最亮的快速電波爆發,訊噪比(Signal to Noise ratio,縮寫S/N)數值達到驚人的 411。

作為比較,之前記錄的快速電波爆發最高訊噪比只有 90,其餘快速電波爆發的訊噪比通常小於 20。

多數天文學家仍保守推論快速電波爆發可能來自黑洞或中子星碰撞,但也有另一派學者認為是外星文明,比如哈佛大學物理學家 Avi Loeb 於去年一篇論文中提到,快速電波爆發可能是外星太空船使用能量光束作為推進動力時的產物。

總之,即使快速電波爆發無法追蹤,統計資料還是可能告訴科學家更多訊息,比如瞭解 FRB 的發生頻率。

We Just Caught The Strongest-Ever Fast Radio Burst, But They're Still Super Mysterious

Three more of the mysterious fast radio burst (FRB) signals have been detected this month, and one of them is a real record-breaker, coming in with the highest signal-to-noise ratio ever recorded. That makes it the "brightest" FRB that's ever been observed.

The signals came in on March 1, March 9 (that's the really bright one) and March 11, snagged by the Parkes Observatory radio telescope in remote Australia.

They are called FRB 180301, FRB 180309 and FRB 180311, following the fast radio burst convention of being named for the dates on which they occurred.

Fast radio bursts have become one of the most fascinating mysteries in space. They've only been detected from 33 sources in total, and only in the last few decades. One of those sources, FRB 121102, is unique in that it repeats. But most FRB sources only flash once, and then they're gone.

Each flash, a powerful radio signal generating as much energy as hundreds of millions of Suns, lasts just milliseconds, with no warning. They are therefore impossible to predict and, because the majority of them don't repeat, impossible to trace to a source.

FRB 121102 is the exception, and may help narrow down a phenomenon that causes fast radio bursts, but there are many theories - and it's entirely possible that there is more than one explanation.

The most recent research into FRB 121102 suggests its source is a neutron star, but other hypotheses include black holes, pulsars with companion stars, imploding pulsars, a type of star called a blitzar, a connection with gamma-ray bursts (which we now know can be caused by colliding neutron stars), and magnetars emitting giant flares.

It's not impossible that they could be engines firing on giant alien spaceships, either, according to a Harvard physicist. However, because they cover a spread of frequencies, they seem to be coming from very far away - possibly billions of light-years. This suggests that whatever is causing them has to be extremely energetic.

As with most other fast radio burst sources, the three from March - including FRB 180309, which has a signal-to-noise ratio four times higher than the previous brightest FRB - are not likely to be repeaters.

However, recording three fast radio bursts in one month is a pretty magnificent haul, considering how few have been detected to date.

Some researchers believe that most FRBs are actually repeaters, it's just that most of the signals they emit are too faint for us to detect.

An upcoming radio telescope project could help figure that out. The Australian Square Kilometre Array Pathfinder, which detected three fast radio bursts last year after it was switched on for the first time, is the pathfinder for the powerful Square Kilometre Array, being built across Australia, New Zealand and South Africa.

The SKA will include a low-frequency aperture array which may be able to capture those lower-frequency signals - if they exist. But the telescope will also cover a much wider area of the sky, in much greater detail, which means that fast radio burst discoveries may occur much more often.

Even if they are untraceable, that statistical data could potentially help tell us more about them. At the very least, we could learn how frequently FRBs are occurring.

So watch this space.

https://www.sciencealert.com/brightest-fast-radio-burst-ever-detected-parkes-observatory-frb-180309