The great stellar dimming of T Tauri has begun

The story of how our own Sun was born remains a cosmic mystery.

This glimpse into the stars found in the densest region of the Orion Nebula, near the heart of the Trapezium Cluster, shows a modern glimpse inside a star-forming region of the Milky Way. However, star-formation properties vary over cosmic time, from galaxy to galaxy, at different radii from the galactic center, etc. All of these properties and more must be reckoned with to compare the Sun with the overall population of stars within the Universe. Note that our Sun, born 4.6 billion years ago, is younger than 85% of all stars.

Formed 4.6 billion years in the past, we can only see what presently survives.

Although we now believe we understand how the Sun and our Solar System formed, this early view of our past, protoplanetary stage is an illustration only. While many protoplanets existed in the early stages of our system’s formation long ago, today, only eight planets survive. Most of them possess moons, and there are also small rocky, metallic, and icy bodies distributed across various belts and clouds in the Solar System as well.

But elsewhere in the galaxy, Sun-like stars form continuously.

This animation switches between an optical view of the dark molecular cloud that houses protostar L1527 (red circle), and infrared data from the WISE mission that showcases the protoplanetary system and its outflows directly. Many protostars are analogues of Sun-like stars, except they show us what our Sun may have been like 4.6 billion years ago: back when it was first forming.

One young example, T Tauri, became notable in the mid-1800s.

This expansive view of the T Tauri system and its surroundings reveals T Tauri itself next to a bright shining nebula: NGC 1555. Although other bright stars abound, not visible here are T Tauri (North)’s two trinary companions: T Tauri South a and b. Those two stars have a dusty disk around them, which may have begun passing in front of T Tauri North in recent years only.

Not only does its brightness vary with time, but a nearby nebula shows variability as well.

This three-color image of T Tauri and its surrounding environment (with the variable nebula NGC 1555) was acquired with the Gemini North telescope on Mauna Kea. As the star brightens and faintens, so does the nearby nebula, which shines due to the reflected light from the star T Tauri North.

These emission line-rich, variable stars represent young Sun-like stars: under 3 million years old.

This view of protostar L1527 shows the NIRCam and MIRI views from JWST rotated and stretched in order to transition between them. Although both views showcase important features of the outflows from this object, near-infrared and mid-infrared wavelengths are sensitive to different features: gas, dust, molecules, and more.

In 1980, an infrared companion star was discovered: T Tauri South.

This image of the T Tauri system takes advantage of adaptive optics and uses the Canada-France-Hawaii telescope. While T Tauri North is prominent, hints of T Tauri South’s two stellar components can be spotted poking out in the data as well.

Then, in 1997, T Tauri South was shown to be a binary, making T Tauri a triplet system.

This image of the T Tauri system, from the Hubble Space Telescope, is overlaid with infrared flux contours in red, showing the positions of all three components of the T Tauri system: T Tauri North, T Tauri South a, and T Tauri South b. A circumbinary ring around T Tauri South a and b creates a silhouette in the ultraviolet data.

The “southern” binary, shrouded in a ring of dusty material, is completely blocked in visible light.

This set of Hubble observations of the T Tauri system contains no infrared light, but instead focuses on ultraviolet emissions. The star T Tauri North is clearly visible, as are extended emission features. The T Tauri South component, consisting of two stars, appears as a dark dust lane only, as both ultraviolet and optical light are extincted, or blocked off, so significantly that no emissions can get through the circumbinary disk.

The original, now called T Tauri North, remained at a constant brightness from 1970-2016.

This data shows the light-curve for T Tauri (North): the optically visible component of the T Tauri triple system. First recorded in the mid-1800s, it was highly variable throughout the 1800s but became a source of steady brightness throughout the 20th and early 21st centuries. The very recent past, however, has shown a re-dimming.

Then, starting in 2017, T Tauri North began dimming significantly.

Although the brightness of T Tauri North was steady for about 46 years, at magnitude 10.5 or so, a recent series of observations have shown that, since 2017, it has faintened by around 2 astronomical magnitudes. This has been theorized to be due to an “overlapping” of the circumbinary disk around T Tauri South with the line-of-sight to T Tauri North.

Why? Because the dusty disk around the T Tauri South binary is passing in front of it!

This ultraviolet (blue) and infrared (yellow) composite image of the T Tauri system from ~20 years ago shows the circumbinary ring around T Tauri South projected with a red line, with the expected migration path traced out at right. The circumbinary disk overlapping with T Tauri North’s position should coincide with the start of a new dimming event.

Predicted back in 2003, this dimming, and reddening, is now occurring.

This graph shows the time-evolution of different color filters, and their intensity differences, as a function of time for the star T Tauri North. The evolution of the color differences points to a recent reddening: consistent with the new appearance of a foreground population of dust.

As the obscuration intensifies, T Tauri North may disappear completely in visible light.

This three-panel set shows the observations of the T Tauri system in 2004 (left) and 2019 (middle), with the differences in the dust distribution of neutral oxygen (left) highlighted in the third panel.

Absorption spectroscopy will study T Tauri South’s circumbinary disk: revealing its density, depth, and composition.

The observed optical dimming of T Tauri North is thought to be due to a circumbinary disk around the T Tauri South binary system passing in front of T Tauri North as seen from our position. Over the next ~100 years, the dimming should intensify, rendering T Tauri North potentially invisible at visible light wavelengths.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.