参宿四的极度昏暗被归咎于一个尘土飞扬的喷嚏

参宿四的极度昏暗被归咎于一个尘土飞扬的喷嚏

Between September last year and this February, red supergiant Betelgeuse experienced an unprecedented dimming period that led the supergiant to drop out of the Top 20 brightest stars in the night sky.

从去年9月到今年2月，红巨星参宿四经历了一段前所未有的变暗期，导致这颗超级巨星从夜空中最亮的20颗恒星中消失。

Betelgeuse's activity led to speculation it was hinting at its impending supernova. However, as a variable star, Betelgeuse experiences changes in its brightness every 420 days, and this current dimming fits with this just being an extra-strong cycle. Why it reached such an exceptionally low luminosity, dropping to around 40 percent of its usual brightness, is still curious. Now researchers have a new theory, blaming it on a release of dust from its outer layers; basically, a sneeze.

参宿四的活动导致人们猜测它是在暗示即将发生的超新星。然而，作为一颗变星，参宿四每420天经历一次亮度的变化，而当前的调光正好与这一超强周期相吻合。为什么它的光度会降至如此低的水平，只有平常亮度的40%左右，我们仍然很好奇。现在研究人员有了一种新的理论，认为这是由于其外层释放出的灰尘;基本上,一个喷嚏。

Alfredo Carpineti

A new paper, accepted in the Astrophysical Journal Letters, points out that the temperature of the star has changed marginally during this period and it is, in fact, warmer than it should be if its dimming was caused by the star's cooling surface. Instead, they think the star got rid of some of its material from its outer layers, which is blocking the light.

发表在《天体物理学杂志通讯》上的一篇新论文指出，在此期间，这颗恒星的温度发生了微小的变化，事实上，如果它的变暗是由恒星的冷却表面造成的，那么它的温度就比应该的温度要高。相反，他们认为这颗恒星摆脱了外层阻挡光线的物质。

“We see this all the time in red supergiants, and it’s a normal part of their life cycle,” lead author Professor Emily Levesque from the University of Washington said in a statement. “Red supergiants will occasionally shed material from their surfaces, which will condense around the star as dust. As it cools and dissipates, the dust grains will absorb some of the light heading toward us and block our view.”

研究报告的主要作者、华盛顿大学的埃米莉·莱维斯克教授在一份声明中说:“我们在红巨星身上经常看到这种现象，这是它们生命周期中很正常的一部分。”“红巨星偶尔会从它们的表面脱落物质，这些物质会在恒星周围凝结成尘埃。当它冷却并消散时，尘埃颗粒会吸收部分射向我们的光线，从而挡住我们的视线。”

Levesque and her co-author Philip Massey were part of the team who had previously estimated the temperature of the surface of the star in 2004. They took observations on February 14 2020 to estimated how much Betelgeuse had cooled down. It turned out, not very much at all. The average surface temperature of the star is 3,325 °C ( 6,017 °F). That’s only between 50-100°C (90-180°F) cooler than the previously estimated temperature.

莱维斯克和她的合著者菲利普·梅西曾在2004年估算过这颗恒星表面的温度。他们在2020年2月14日进行了观测，以估计参宿四冷却了多少。结果是，变化并不大。该恒星的平均表面温度为3325°C(6017°F)。这只是比之前估计的温度低了50-100°C(90-180°F)。

“A comparison with our 2004 spectrum showed immediately that the temperature hadn’t changed significantly,” said Massey. “We knew the answer had to be dust.”

Massey说:“与我们2004年的光谱相比，温度并没有明显的变化。我们知道答案肯定是灰尘。”

Clouds of dust have been observed around other stars as well and the team is confident that new observations of Betelgeuse will reveal them here as well. However, this is only one reason to continue looking at this star. Betelgeuse is the nearest red supergiant to Earth and it is a perfect laboratory to work out how these celestial bodies evolve.

在其他恒星周围也观察到了尘埃云团，研究小组相信，对参宿四的新观测也将在这里揭示这些云团。然而，这只是继续观察这颗恒星的一个原因。参宿四是离地球最近的红色超级巨星，它是研究这些天体如何演化的完美实验室。

“Red supergiants are very dynamic stars,” said Levesque. “The more we can learn about their normal behavior — temperature fluctuations, dust, convection cells — the better we can understand them and recognize when something truly unique, like a supernova, might happen.”

“红巨星是非常活跃的恒星，”莱维斯克说。“我们对它们的正常行为——温度波动、尘埃、对流细胞——了解得越多，我们就能更好地理解它们，并更好地识别什么时候可能会发生真正独特的事情，比如超新星爆炸。”