astronomy

Gliese 229

Gliese 229 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 Gliese 229 rather than just read about it. In short: Gliese 229 (also written as Gl 229 or GJ 229) is a multiple system composed of a red dwarf and two brown dwarfs, located 18.8 light-years away. It is the nearest star system in the constellation Lepus.

Key takeaways

Gliese 229 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Gliese 229 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Gliese 229 from memory before moving on to harder problems.

Reference excerpt

Gliese 229 (also written as Gl 229 or GJ 229) is a multiple system composed of a red dwarf and two brown dwarfs, located 18.8 light-years away. It is the nearest star system in the constellation Lepus. The primary component has 58% of the mass of the Sun, 55% of the Sun's radius, and a very low projected rotational velocity of 1 km/s at the stellar equator.

Red dwarf

Gliese 229 is known to be a low-activity flare star, which means it undergoes random increases in luminosity because of magnetic activity at the surface. The spectrum shows emission lines of calcium in the H and K bands. The emission of X-rays has been detected from the corona of this star. These may be caused by magnetic loops interacting with the gas of the star's outer atmosphere. No large-scale star-spot activity has been detected. The space velocity components of this star are U = +12, V = –11 and W = –12 km/s. The orbit of this star through the Milky Way galaxy has an eccentricity of 0.07 and an orbital inclination of 0.29°.

Brown dwarfs

A substellar companion was discovered in 1994 by Caltech astronomers Kulkarni, Tadashi Nakajima, Keith Matthews, and Rebecca Oppenheimer, and Johns Hopkins scientists Sam Durrance and David Golimowski. It was confirmed in 1995 as Gliese 229B, It was one of the first brown dwarfs discovered. Although too small to sustain hydrogen-burning nuclear fusion as in a main-sequence star, with a mass of around 40 to 60 times that of Jupiter (0.06 solar masses), it is still too massive to be a planet. As a brown dwarf, its core temperature is high enough to initiate the fusion of deuterium with a proton to form helium-3, but it is thought that it used up all its deuterium fuel long ago. This object has a surface temperature of 950 K. Gliese 229B is the prototype of the T dwarfs, due to the detection of methane in its spectrum. It also shows other molecules in its atmosphere, namely water vapor, carbon monoxide and ammonia. Atomic absorption lines of caesium, sodium and potassium are also detected. Gliese 229 B was later found to be a binary brown dwarf. Since 2021 it was suggested to be an unresolved binary, given the inconsistency between the object's measured mass and luminosity. Further evidence that Gliese 229B is an equal-mass binary comes from high-resolution spectroscopy from the Subaru Telescope. Gliese 229 B was then finally resolved in 2024 with VLT/GRAVITY and VLT/CRIRES+. The components are called Gliese 229 Ba and Gliese 229 Bb. The pair is a tight orbit with an orbital period of 12.1 days and a semi-major axis of 0.042 astronomical units (about 16 Earth-Moon distances). The changes in radial velocity extracted from CRIRES+ helped to resolve the orbit of Gliese 229B. The binary has an inclination of 31.4°±0.3° and an eccentricity of 0.234±0.004. The inclination of the binary is misaligned by 37+7−10° in respect to the orbit of Gliese 229B around Gliese 229A. Additional radial velocity changes between two epochs were detected in Gliese 229B with Keck NIRSPEC. This team independently discovered the binarity of Gliese 229B. The brown dwarf pair was observed with the James Webb Space Telescope's MIRI low-resolution spectroscopy. Previous works showed a difference in abundances between host star and companion in Gliese 229 from near-infrared spectra. This new study using mid-infrared data showed that the pair has abundances consistent with the host star. The metallicities were measured to be C/O = 0.65±0.05 and [M/H]=0.00+0.04−0.03 and are equal for each brown dwarf in the pair. The host star has C/O = 0.68±0.12 and [M/H] = −0.02±0.06.

Search for planets In March 2014, a super-Neptune mass planet candidate was announced in a much closer-in orbit around GJ 229. Given the proximity of the Gliese 229 system to the Sun, the orbit of GJ 229 Ab might be fully characterized by the Gaia space-astrometry mission or via direct imaging. In 2020, a super-Earth mass planet was discovered around GJ 229. GJ 229 Ac orbits the star closer in than GJ 229 Ab, located towards the outer edge but still well inside the star's habitable zone and in that sense similar to Mars in our own Solar System. While considering GJ 229 Ab unconfirmed, the study estimated a significantly lower minimum mass for it. However, a more recent study found that when stellar activity was taken in account, the radial velocity signals corresponding to the planets' orbital periods disappeared. Therefore, intrinsic activity of the host star or errors in the previous observations are the cause of the radial velocity variations, instead of planets, which mean Gliese 229 Ab and Gliese 229 Ac likely do not exist.

Illustrations

Worked examples

Example 1 — a first encounter with Gliese 229

Start with the simplest possible case. Write down what Gliese 229 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 Gliese 229 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 Gliese 229 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 Gliese 229

In research: Gliese 229 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 Gliese 229 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: Gliese 229 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1994, Binary stars, Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for Gliese 229 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 Gliese 229 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gliese 229 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 Gliese 229 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Gliese 229 in simple terms?

Why does Gliese 229 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 Gliese 229?

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 Gliese 229.