The largest planetary construction site ever seen, spanning hundreds of billions of miles in size, may well be cast in a huge shadow that accentuates its strange appearance. In short, it looks like a space butterfly – and it was ignored for years.
The object, known as IRAS 23077+6707, was originally cataloged as an infrared emission source by the Infrared Astronomy Satellite (IRAS) in the 1980s. Then in 2016, while conducting research on active galaxies in the region of the constellation Cepheus, astronomer Cyprian Bergea of the US Naval Observatory accidentally rediscovered it with the Pan-Star Telescope and Rapid Response System (Pan-STARRS).
Bergea wasn’t sure what it was, but it appeared to have two parallel sheets with a dark stripe between them—typical of a planet-forming disc with an edge. The bright parts in such an object represent light scattered by dust in the upper echelons of the disc, while the dark band is the equivalent of our solar systemthe plane of the ecliptic where most of the material is concentrated. It is this dense patch of material that blocks and absorbs the light of the system’s central star. The upper and lower planes of the disk spread out gradually instead of showing a sharp edge, while two filaments trace these expanded parts, which are also expanded. Because of all this, the arrangement looks strangely like a butterfly – but in a way, these bright areas separated by a dark street also give the impression of a hamburger. So, in keeping with his Romanian heritage, having grown up near Transylvania, Bergea named IRAS 23077+6707 Dracula’s Chivito,” chivito is a hamburger-like sandwich from his native country.
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Now, thanks to observations with the Submillimeter Array (SMA) in Hawaii, astronomers, including Berghea, have confirmed that this particular chivito is indeed a planet-forming disk seen edge-on, but it’s no ordinary disk. It is the most massive planet-forming disk ever seen.
“What we found was incredible – evidence that this is the largest planet-forming disk ever discovered. It is extremely rich in dust and gas, which we know are the building blocks of planets,” said Christina Monsch, an astronomer at the Harvard…Smithsonian Center for Astrophysics, in a statement. Monch is the lead author of one of two new papers describing the disk.
To give an idea of the scale of this particular world-building yard, astronomers estimate it to be somewhere between 800 and 1000 light years far based on the fact that it is located in the sky near the Cepheus star-forming region. If correct, then the angular size of the disk in our sky corresponds to the radius of the disk, which is thousands astronomical units (AU). To provide further context, one AU is defined as the average distance between The Earth and on sunor 149.6 million kilometers (93 million miles), while the outermost known planet, Neptuneis 30 AU from our sun.
“From the SMA data, we can also weigh the dust and gas in this planetary nursery, which we found has enough material to form many giant planets — and at distances over 300 times the distance between the Sun and Jupiter!” said Monche.
What’s more, the disc spins. The SMA measures radio waves emitted by carbon monoxide gas in the disc, and some of these radio waves are with redshift, indicating that they are emitted by clouds of gas moving away from us; meanwhile, submillimeter radio waves from carbon monoxide in other parts of the disk were blue-shifted, meaning they were moving toward us. This behavior is a hallmark of a rotary system.
“The SMA data offer us smoldering evidence that … it orbits a star probably two to four times more massive than our own sun,” Monsch said. It is possible that this star is still growing as material from the disk falls inward and accumulates on it.
Besides the huge size of the disk, another peculiar aspect is that the western lobe of the disk is noticeably darker than the other lobe by a factor of six. Monsch, Berghea and their colleagues aren’t sure why this is, but there are some possibilities being considered. One strong candidate is that it’s just an illusion that the two halves are unequal in brightness, a geometric effect caused by the disc not being perfectly edge-on for us, so we can see a bit more of the eastern half than the western half.
But there is another explanation, which is that half of the disk is in shadow.
This suggests that the disc, rather than being pregnant with planetary potential, has already given birth and that a giant planet is now plowing through the disc. This planet can sweep up raw material as it grows, carving out a ring path or gap in the disk in the process.
Such a gap would effectively split the disc, leading to instability that would cause the inner disc to warp like a vinyl record that has been bent too much. This discrepancy would block some of the light from the central young star, causing the inner disk to cast a shadow on the outer disk. Therefore, the asymmetry in the brightness of the studied disk can be indirect evidence of the presence of a giant planet. Fittingly, IRAS 23077+6707 bears some resemblance to the shape of a butterfly; just as a caterpillar enters a chrysalis and emerges as a butterfly, the chrysalis of a protoplanetary disc may allow gas and dust—the remnants of ancient generations of stars — to reform and blossom into space butterflies on new planets.
And on top of all that, the existence of IRAS 23077+6707 raises a nagging question. Computer simulations predict that we should see more edge-on planet-forming disks than we actually do—so are there more supermassive disks we haven’t yet recognized?
The observations of IRAS 23077+6707 are reported in two papers, one published May 14 in The Astrophysical Journal Lettersand another which has been accepted for publication in a future issue of the same journal.
