Astronomers discover giant mid-infrared outburst from distant young stellar object

Chinese astronomers, while conducting a blind search for significant mid-infrared variables using the Wide Infrared Sky Explorer (WISE) archive, stumbled upon a remarkable discovery. They found a massive mid-infrared outburst originating from a distant young stellar object named J064722.95+031644.6. This discovery, detailed in a paper published on September 20, 2023, on the pre-print server arXiv, sheds light on the intriguing behavior of young stars in their early stages of evolution.

Young Stellar Objects (YSOs) represent stars in the initial phases of development, including protostars and pre-main sequence stars. Typically, YSOs are observed within dense molecular clumps, which are rich in molecular gas and interstellar dust.

One of the fascinating aspects of YSOs is their susceptibility to episodic accretion processes, which can lead to accretion-driven outbursts. These events are categorized into two main types: EX Lup (or EXors) outbursts, which are relatively modest in magnitude and last from months to a couple of years, and FU Ori (or FUors) outbursts, which are more extreme and rare. FUors can exhibit magnitudes up to five to six times brighter and can persist for decades to even centuries.

J064722.95+031644.6, abbreviated as J0647, was initially identified as an infrared source near a star-forming region in the Monoceros constellation. However, its true nature remained a mystery until a recent study led by Tinggui Wang from the University of Science and Technology of China in Hefei.

Wang’s team conducted an examination of mid-infrared light curves using data from the W1 and W2 bands of the AllWISE and NEOWISE photometric databases in the Infrared Science Archive (IRSA), pinpointing J0647 as a YSO that experienced a massive mid-infrared outburst.

The researchers reported, “In this paper, we report the serendipitous discovery of a gigantic eruption in a previously unknown YSO (RA = 06:47:22.95, DEC = +03:16:44.56) in the mid-infrared.”

The study reveals that J0647 is a Class I YSO, deeply embedded and possessing both a disk and an envelope. Its quiescent luminosity is approximately 9.0 times that of the Sun, and its estimated mass falls within the range of 0.58 to 1.3 solar masses.

During the mid-infrared outburst, J0647’s brightness gradually increased by a factor of 5 from 2014 to 2016, followed by a sudden surge by more than 100 times in 2017. This implies that the YSO exhibited a remarkable 500-fold increase in mid-infrared brightness over a span of two years, followed by a gradual decline. Notably, this eruption’s amplitude is the second largest ever recorded among all known YSO eruptions in the mid-infrared range.

Based solely on its light curve, astronomers classified J0647 as an intermediate-type eruption YSO with an exceptional amplitude. Its near-infrared spectrum differs from classical FUors, EXors, or other intermediate-type outbursts in YSOs due to the absence of absorption or emission lines, except for diatomic hydrogen (H2).

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