This object-orbiting event was discovered in a young binary star system, Z Star Canis Major (Z CMa), about 3700 light-years away from Earth (Figure 1). Infrared observations with the Subaru Telescope and other telescopes have revealed a protoplanetary disk surrounding the binary system and an elongated tail-like structure within it (Hawaii Observatory 2016 Observation Results).The ALMA telescope has discovered a new object at the end of this “tail,” about 5000 astronomical units (5000 times the distance between the Sun and Earth) from the binary star.

When celestial bodies encounter each other, they cause vortices, distortions, gaps, and other changes in the disk’s morphology that can be seen as traces of the flyby. By carefully observing the disk of Z CMa, scientists have identified multiple traces of the flyby.

These traces not only helped to validate the celestial flyby, but also led us to consider what the “visit” might mean for the future of Z CMa and the planets born in that system. Flyby events can dramatically alter the protoplanetary disk, the cradle of planetary birth, just as a long “tail” was created around Z CMa. Another possible effect on the central star is the known explosive brightening of the central star in Z CMa due to the sudden outpouring of gas from the disk, which may have been facilitated by the disturbance of the disk by the flying object. As a result, the development of the entire star system may also be affected in ways that have not yet been observed.

Dr. Ruobing Dong (University of Victoria), who led the study, noted that studying the evolution and growth of young star systems throughout the galaxy will also help us better understand the origin of our solar system. Studying these events gives us an insight into the past history of how our solar system developed,” he said. Seeing these events occur in newly formed systems gives us the information we need to say, ‘Oh, this could have happened a long time ago in our solar system.’

Z CMa has long attracted attention as a mysterious variable-light object, but we were surprised to see it in this form,” says co-researcher Professor Motohide Tamura (University of Tokyo/National Institutes of Natural Sciences, Center for Astrobiology). The sharp observations by Subaru, ALMA, and VLA at multiple wavelengths, combined with the latest theoretical research, enabled us to successfully capture this unusual flyby phenomenon that occurred on a newly born star.

For more information, please refer to the Press release article from the National Radio Astronomy Observatory (NRAO).


This research result was published in Nature Astronomy on January 13, 2022 (Ruobing Dong et al. “A likely flyby of binary protostar Z CMa caught in action“)。

About Subaru Telescope
Subaru Telescope is a large optical-infrared telescope operated by the National Astronomical Observatory of Japan (NAOJ) and supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) under the Large-Scale Scientific Frontier Initiative. Mauna Kea, where Subaru Telescope is located, is a precious natural environment and an important place in Hawaiian culture and history, and we are deeply grateful for the opportunity to explore the universe from Mauna Kea.

■Related Links

• ALMA catches “intruder” redhanded in rarely detected stellar flyby event (NRAO 13 Jan 2022, Press Release)
• Subaru Telescope January 13, 2022 Press Release

The post Stellar Visitors Shaking the Cradle of Planet Formation first appeared on Astrobiology Center, NINS.

Summary

An international research team including researchers from the Astrobiology Center, National Astronomical Observatory of Japan, and Tokyo Institute of Technology observed the extra-solar system K2-290 with two planets and a companion star using Subaru Telescope and other instruments, revealing that the planet has a retrograde orbit to K2-290’s rotation.

In planetary systems outside the solar system, it is observationally known that the orbital direction (or axis of revolution) of planets often significantly differs from the rotation direction (axis of rotation) of the central star. Various mechanisms, such as gravitational scattering between planets or the influence of nearby stars’ gravity, have been proposed to induce such offsets, but the exact causes were previously unclear.

The observed K2-290 is a star with two well-aligned exoplanets, and observations including Subaru Telescope revealed that the orbital directions of these two planets are retrograde relative to the rotation direction of the central star. On the other hand, previous high-resolution imaging observations with Subaru Telescope confirmed the presence of a companion star (a low-mass star outside the planetary system) orbiting K2-290. Based on these facts, numerical simulations indicate that the original protoplanetary disk at which the planets formed was tilted by the gravity of the companion star, leading ultimately to the formation of retrograde planets. This is the first confirmation of evidence of significant changes in the disk plane by a companion star during the planet formation phase.

For more details:

Subaru Telescope Press Release
Aarhus University Press Release

The post Discovery of Evidence for a Flipped Protoplanetary Disk first appeared on Astrobiology Center, NINS.

Abstract:

A research group, including researchers at the Astrobiology Center, led by Project Assistant Professor Takashi Tsukagoshi at the National Astronomical Observatory of Japan, observed a circumstellar disk of dust and gas (protoplanetary disk) around a young star TW Hydrae, and discovered compelling evidence within the disk suggesting planet formation. Specifically, they identified a small radio source within the disk that had not ever been detected. The research group speculate that this radio source could be either 1) a “circumplanetary disk” surrounding a Neptune-sized planet with ongoing formation or 2) a dusty structure formed by gas accumulations within vortices in the disk that could turn into planets in the future. In either scenario, this observation represents a crucial step in witnessing the vital processes of planet formation within the disk, enhancing our understanding of planet formation processes.

Research Background

In recent years, many planets of great diversity have been discovered around non-solar stars. Planets are thought to be born in a disk of dust and gas (protoplanetary disk) surrounding a young star. However, many details of the birth and growth process of a planet, such as how exactly the planet grows by incorporating the surrounding material, remain unresolved. Astronomers are trying to understand how planets are born by observing protoplanetary disks in detail.

How are planets formed in protoplanetary disks? Initially, protoplanetary disks are composed of microscopic dust particles ranging from a few micrometers to a few millimeters in diameter. Over time, this dust coalesces and grows into a rocky mass called a microplanet. This is the seed of a planet. The rocky mass thus created grows and eventually becomes a planet, taking in dust and gas from its surroundings due to its own gravity. Theoretical calculations predict that the material being incorporated will form a disk-like structure that rotates around the planet. This disk-like structure is called a periplanetary disk. The size of the disk is thought to be very small, about 1% of the total size of the protoplanetary disk.

Finding “periplanetary disks formed in protoplanetary disks” is one of the most important themes in the study of the formation process of planetary systems. However, we have not been able to find a periplanetary disk in our previous observations. Recent observations with the ALMA telescope have revealed dust collecting in protoplanetary disks (Note 1), but these disks are too large to be considered periplanetary disks.

High-Resolution, High-Sensitivity Observations with ALMA Telescope

Takashi Tsukagoshi, Project Assistant Professor at the National Astronomical Observatory of Japan, and his research team observed the young star TW Hydrae using the ALMA telescope in order to study the detailed process of planet formation. The star TW Hydrae is estimated to be approximately 10 million years old. Located 194 light years from Earth, it is the closest of these young stars to our solar system. Since TW is as massive as the Sun, it has been the subject of numerous observations as a possible clue to the origin of our solar system.

It is well known from previous observations that a protoplanetary disk exists around TW Hydrae. Dust and gas in protoplanetary disks do not emit visible light because of their extremely low temperature of about -250°C. On the other hand, radio waves are emitted from low-temperature materials. On the other hand, radio waves are emitted from low-temperature materials, so they have been actively observed with the ALMA telescope, which is capable of capturing radio waves. As a result, it is known that the disk has a structure with multiple gaps (Note 2). Disks have a symmetrical structure around the center, and small structures such as periplanetary disks associated with forming planets have not been found until now.

Observation Results

The sensitivity of this observation is about three times higher than that of previous observations with the ALMA telescope, and succeeded in obtaining a more detailed distribution of radio wave intensity within the disk.

As a result, only one small radio source was discovered in the protoplanetary disk, which had not been found before. The source was located on the southwest side of the disk, 52 AU(*3) from the center of the protoplanetary disk, where the radio waves were 1.5 times stronger than those in the surrounding area. The radio source extends slightly in the direction of disk rotation and is about 4 AU long and 1 AU wide. This is the first time such a small radio source has been found in a protoplanetary disk.

What is the identity of this small radio source? There are two main possibilities.

One possibility is that it is a circumstellar disk. The size of the structure discovered suggests that if it is a periplanetary disk, a Neptune-mass planet has already formed at its center.

In fact, previous observations have shown that a Jupiter-mass planet would not exist at a distance of 52 AU from TW Hydrae. One of the reasons for this is infrared observations. Heavy planets in protoplanetary disks glow brightly in the infrared because they collect gas from the surrounding protoplanetary disks. However, no such infrared point source has been confirmed by previous observations. Another reason is the absence of a gap in the disk 52 AU from the central star. It is thought that a heavy planet would create a gap by exerting gravity on the surrounding protoplanetary disk, but no such structure has been found in previous observations.

Based on the above facts, it is thought that there are no Jupiter-mass heavy planets in this disk, but due to the sensitivity limitations of the observations, nothing could be said yet about whether there are Neptune-mass light planets in the disk. This time, by taking advantage of the high sensitivity and resolution of ALMA, we were able to detect weak radio emissions, and thus clarify the possibility of the existence of a lighter planet.

On the other hand, the observed radio wave strength is a little too strong to be considered a periplanetary disk surrounding a Neptune-sized planet. In addition, the observed radio source was elliptical in shape, whereas a circumplanetary disk would be assumed to be circular with the planet at its center. Therefore, there is a possibility that the radio source is dust accumulated in a small gas vortex. Just as high and low pressure systems occur on Earth, there are thought to be many localized swirling currents in protoplanetary disks, where dust is swept up and collected. This is an important structure for the first stage of dust coalescence into a planet. Theory predicts that the dust trapped in the vortex will spread out in an elliptical shape, which is consistent with the structure of the radio source found by this observation. On the other hand, the presence of only one such small-scale anticyclone in a protoplanetary disk is a bit unnatural.

Thus, there are parts that are consistent with observations and parts that are unnatural in both the “periplanetary disk theory” and the “gas vortex theory,” and we were unable to determine the identity of the source in this research. However, whether it is a circumstellar disk or dust trapped in a vortex, this research is very significant in that it is the first time that we have pinpointed an important part of the planet formation process.

Developments for Future Research

In order to determine the identity of the small radio source discovered in this study, the research group aims to more directly capture signs of a planet in formation. Tsukagoshi explains, “The inner edges of periplanetary disks are particularly warm, as the temperature of forming planets increases as they take in material from their surroundings. We hope to use ALMA to obtain higher resolution observations to determine the temperature distribution inside the radio source discovered this time and to confirm whether there is a planet at the center of the source. We are also preparing to use the Subaru Telescope to observe the light emitted when the hydrogen around the planet becomes hot. He added.

Publication Information：

Note 1: For example, crescent and spiral clusters of dust have been found around the young star MWC 758. (Reference: Research result published on June 21, 2018, “Planet birth site with diverse structures – high-resolution observations of the young star MWC 758”)

Note 2: See the research results published March 31, 2016, “First Observation of the Birth Site of a Planet with an Earth-like Orbit Around a Young Star” and the press release published September 14, 2016, “Captured the Formation Site of a Giant Ice Planet – Evidence of Neptune-sized Planet Formation Found with ALMA Telescope –” and others.

Note 3: 1 AU corresponds to the average distance between the Earth and the Sun, which is about 150 million kilometers. 52 AU corresponds to about 1.7 times the orbital radius of Neptune in the solar system.

Paper and Research Team:

The observational achievements were published in the astronomical journal “The Astrophysical Journal Letters” on June 10, 2019, with the title “Discovery of an au-scale excess in millimeter emission from the protoplanetary disk around TW Hya.”

The research team member involved in this study are as follows:

Takashi Tsukagoshi (National Astronomical Observatory of Japan)
Takayuki Muto (Kogakuin University)
Hideko Nomura (National Astronomical Observatory of Japan / Tokyo Institute of Technology)
Ryohei Kawabe (National Astronomical Observatory of Japan / SOKENDAI / the University of Tokyo)
Kazuhiro Kanagawa (the University of Tokyo)
Satoshi Okuzumi (Tokyo Institute of Technology)
Shigeru Ida (Tokyo Institute of Technology)
Catherine Walsh (University of Leeds)
Tom J. Millar (Queen’s University Belfast)
Sanemichi Takahashi (National Astronomical Observatory of Japan / Kogakuin University)
Jun Hashimoto (Astrobiology Center)
Taichi Uyama (California Institute of Technology / the University of Tokyo / National Astronomical Observatory of Japan)
Motohide Tamura (the University of Tokyo / Astrobiology Center)

This research was supported by the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (No. 17K14244, 17H01103, 18H05441, 19K03932) and STFC (ST/P000321/1, ST/R000549/1).

Related Links：

National Astronomical Observatory of Japan Press Release

The post ALMA Telescope Identifies the Specific Location of Planet Formation first appeared on Astrobiology Center, NINS.

The clear images from SCExAO show that this ‘young solar system’ of LkCa 15 is more like our own solar system than previously thought,” says lead author Thayne Currie of NASA’s Ames Research Center and the National Astronomical Observatory of Japan’s Hawaii NASA Ames Research Center and the National Astronomical Observatory of Hawaii).

LkCa 15, a young solar-type star, has a protoplanetary disk made of planetesimal gas and dust. Previous studies have shown that there are large gaps in this disk. This gap tells us that a “young planet” made of dust is forming in the disk.

However, capturing this planet orbiting LkCa 15 at a distance of more than 500 light years from the Earth directly from the ground on a scale similar to that of the solar system is extremely challenging, even for a large telescope like the Subaru Telescope, which has adaptive optics to compensate for the effects of atmospheric fluctuations of the Earth. Previously, based on observations using a state-of-the-art technique called aperture masking interferometry, three candidate planetesimals were thought to orbit from Saturn to Neptune, which was the first recognized extrasolar planet in the disk. However, this observation method made it particularly difficult to determine how much light was actually coming from the planets compared to the light scattered by the dust disks.

SCExAO on the Subaru Telescope uses a combination of a faster and more sensitive camera than typical adaptive optics instruments and a variable deformable mirror with as many as 2,000 elements. Furthermore, by sending light to a surface spectrograph called CHARIS, it is possible to directly distinguish differences in the “color” of light coming from celestial objects at high resolution, making it possible to study the atmospheric composition of planets and other objects in detail.

SCExAO/CHARIS will allow us to probe planets similar to our own solar system scale more directly than ever before and even reveal their properties,” said Olivier Guyon, SCExAO Instrument Director at NAOJ’s Subaru Telescope in Hawaii.

The SCExAO/CHARIS data now show that most of the light coming from around LkCa 15 originates from the disk, which appears to be an extended arc, and has the same brightness as the previously suggested planet candidates. Follow-up observations with the Keck telescope also confirmed that the shape of this disk’s arc has not changed over time. In other words, the light previously thought to be a signal from the orbiting planet is now found to be well consistent with a motionless structure like the disk.

The planetary system of LkCa 15 is quite complex. Based on aperture masking interferometric imaging data acquired prior to this observation, we also thought there would be three Jupiter-like planets. However, the SCExAO/CHARIS data indicate that the previous signals are coming from the disk itself, and that the planets themselves are fainter and likely hidden within the disk. We will continue to challenge ourselves to find that hidden planet,” Currie said.

It will be quite a challenge to clearly distinguish the light from the disk of LkCa 15 and the light from the planet hidden in that disk. However, we are making definite progress technically, and SCExAO will continue to make improvements. In the near future, we may be able to capture a Jupiter-like planet near Saturn’s orbit in the disk of LkCa 15. And further down the road, the planned 30-meter telescope TMT will be equipped with the technology successfully used in SCExAO to image faint planets orbiting near Mars at lower masses.

The results from cutting-edge imaging instruments such as SCExAO provide clues to better understand the origin and evolution of planetary systems, such as whether the history of our solar system is universal or unique,” said paper co-author Motohide Tamura, Director of the National Institutes of Natural Sciences Director and Professor of the Center for Astrobiology, National Institutes of Natural Sciences.

The research outcomes were accepted for publication in the Astrophysical Journal Letters (Currie et al., “NO CLEAR, DIRECT EVIDENCE FOR MULTIPLE PROTOPLANETS ORBITING LKCA 15: LKCA 15 bcd ARE LIKELY INNER DISK SIGNALS“).Additionally, this study is supported from NASA, the Keck Foundation, the Chilean National Fund for Scientific and Technological Development, and the Japan Society for the Promotion of Science Grants JP18H05442 and JP15H02063.

The post Subaru Telescope Images Hidden Young Planetary Systems first appeared on Astrobiology Center, NINS.