Carnival of Space 404

Astronomers have studied 51 quasars with NASA's Chandra X-ray Observatory and found they may represent an unusual population of black holes that consume excessive amounts of matter, as described in our latest press release. Quasars are objects that have supermassive black holes that also shine very brightly in different types of light. By examining the X-ray properties with Chandra, and combining them with data from ultraviolet and visible light observations, scientists are trying to determine exactly how these large black holes grow so quickly in the early Universe.

The quasars in this study - including the three shown as Chandra images in the bottom of the graphic - are located between about 5 billion and 11.5 billion light years from Earth. These quasars were selected because they had unusually weak emission from certain atoms, especially carbon, at ultraviolet wavelengths. Also, about 65% of the quasars in this new study were found to be much fainter in X-rays, by about 40 times on average, than typical quasars.

Bin Luo has mainly been working on X-ray studies of supermassive black holes in the centers of galaxies. He is now leading the data analysis of the 7-million-second (81 days) Chandra Deep Field-South survey, the deepest Chandra observation ever performed.

Monstrous black holes – quasars fueled by large amounts of gas and dust, consuming of the order of a couple solar masses per year – are known nearly universally to be strong X-ray emitters. Meanwhile, strong line emission – that is, light coming from a narrow range of wavelengths – is also a hallmark of quasar spectra in optical and ultraviolet bands. Therefore, I was quite puzzled when we discovered that a small group of quasars with remarkably weak ultraviolet line emission are often extremely X-ray weak. The pioneering work was led by Jianfeng Wu, Niel Brandt, and Pat Hall in 2011 and 2012, where the X-ray emission from 19 such quasars was examined. What makes things even more interesting is that for a subgroup of these quasars selected with refined ultraviolet properties, almost 100% are weak in X-ray light.