astronomy

TW Hydrae

TW Hydrae is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand TW Hydrae rather than just read about it. In short: TW Hydrae is a T Tauri star approximately 196 light-years away in the constellation of Hydra (the Sea Serpent). TW Hydrae is about 80% of the mass of the Sun, but is only about 5-10 million years old.

Key takeaways

TW Hydrae belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect TW Hydrae to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of TW Hydrae from memory before moving on to harder problems.

Reference excerpt

TW Hydrae is a T Tauri star approximately 196 light-years away in the constellation of Hydra (the Sea Serpent). TW Hydrae is about 80% of the mass of the Sun, but is only about 5-10 million years old. The star appears to be accreting from a protoplanetary disk of dust and gas, oriented face-on to Earth, which has been resolved in images from the ALMA observatory. TW Hydrae is accompanied by about twenty other low-mass stars with similar ages and spatial motions, comprising the "TW Hydrae association" or TWA, one of the closest regions of recent "fossil" star-formation to the Sun.

Stellar characteristics

TW Hydrae is a pre-main-sequence star that is approximately 80% the mass of and 111% the radius of the Sun. It has a temperature of 4000 K and is about 8 million years old. In comparison, the Sun is about 4.6 billion years old and has a temperature of 5778 K. The star's luminosity is 28% (0.28x) that of the Sun, equivalent to that of a main-sequence star of spectral type ~K2. However, the spectral class is K6. The star's apparent magnitude, or how bright it appears from Earth's perspective, is 11.27. It is too dim to be seen with the naked eye.

Planetary system

The star is known to host one exoplanet, TW Hydrae b.

Protoplanetary disk

Previously disproven protoplanet In December 2007, a team led by Johny Setiawan of the Max Planck Institute for Astronomy in Heidelberg, Germany announced discovery of a planet orbiting TW Hydrae, dubbed "TW Hydrae b" with a minimum mass around 1.2 Jupiter masses, a period of 3.56 days, and an orbital radius of 0.04 astronomical units (inside the inner rim of the protoplanetary disk). Assuming it orbits in the same plane as the outer part of the dust disk (inclination 7±1°), it has a true mass of 9.8±3.3 Jupiter masses. However, if the inclination is similar to the inner part of the dust disk (4.3±1.0°), the mass would be 16+5−3 Jupiter masses, making it a brown dwarf. Since the star itself is so young, it was presumed this is the youngest extrasolar planet yet discovered, and essentially still in formation. In 2008 a team of Spanish researchers concluded that the planet does not exist: the radial velocity variations were not consistent when observed at different wavelengths, which would not occur if the origin of the radial velocity variations was caused by an orbiting planet. Instead, the data was better modelled by starspots on TW Hydrae's surface passing in and out of view as the star rotates. "Results support the spot scenario rather than the presence of a hot Jupiter around TW Hya". Similar wavelength-dependent radial velocity variations, also caused by starspots, have been detected on other T Tauri stars.

New study of more distant planet In 2016, ALMA found evidence that a possible Neptune-like planet was forming in its disk, at a distance of around 22 AU.

Outflow of an embedded protoplanet In 2024 observations with ALMA showed sulfur monoxide representing an outflow from an embedded protoplanet. The position of the brightest emission coincides with a planet-carved dust gap at 42 au. Previously this gap was associated with the formation of a super-earth and modelling of the outflow velocity, the researchers estimate a mass of about 4 earth-masses. The mass accretion of this embedded protoplanet is constrained to between 3 ×10−7 and 10−5 MJ/year.

Detection of methanol In 2016, methanol, one of the building blocks for life, was detected in the star's protoplanetary disk.

Gallery

Notes

References

External links

"Hubble's infrared eyes home in on suspected extrasolar planet". NASA. Hubble Space Telescope. Retrieved 2008-06-24. "Notes for star TW Hya and possible planet TW Hya b". Extrasolar Planets Encyclopaedia. Retrieved 2014-01-06.

Illustrations

Worked examples

Example 1 — a first encounter with TW Hydrae

Start with the simplest possible case. Write down what TW Hydrae claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to TW Hydrae before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about TW Hydrae ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of TW Hydrae

In research: TW Hydrae appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses TW Hydrae in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: TW Hydrae is common in secondary-school and first-year university syllabi. It links to neighbouring topics Circumstellar disks, Durchmusterung objects, Hipparcos objects, so understanding it makes those chapters shorter.
In everyday life: Look for TW Hydrae outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study TW Hydrae in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what TW Hydrae means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain TW Hydrae out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is TW Hydrae in simple terms?

Why does TW Hydrae matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study TW Hydrae?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on TW Hydrae.