Detection of galactic center source G2 at 3.8 microns during periapse passage Periapse: The point of a body's elliptical orbit about the system's centre of mass where the distance between the body and the centre of mass is at its minimum. 

• G2 : dusty red object associated with gas that shows tidal interactions as it nears the BH • Observation : test whether G2 is a gas cloud • Keck II LGSAO • NIRC2 : K’[2.1μm] & L’[3.8μm] broadband filters Object & Facility should be tidally disrupted during periapse passage 

Wikipedia: Infrared window • K’[2.1μm] • L’[3.8μm] 

Results • G2 has survived its closest approach to the black hole as a compact, unresolved source at L’ • G2’s L’ brightness measurements are consistent with those over the last decade • G2’s motion continues to be consistent with a Keplerian model. 

Conclusion & Inference • G2 has a central star of ∼30 L⊙, and is surrounded by a large optically thick dust shell(~2.6AU). • L’ and Br-γ emission arises primarily from internal and external heating, respectively. • G2 is a binary star merger product and will ultimately appear similar to the B-stars. 

Introduction • First detected in 2012: 3 M⊕ gas cloud ? Detection: an object(G2) approaching the SMBH Br-γ emission: dusty, 3 earth mass gas cloud If true, it will be disrupted and accreted Interest: can be followed through the predicted accretion 

Introduction • First detected in 2012: 3 M⊕ gas cloud ? • Alternative models: central stellar source • NIR: detectable at L’-M[3-5μm], faint at K’[2μm] • In Br-γ: slightly elongated core, tital tails • New L’ imaging observations of G2 during the closest approach and the following few months 

Result 1 G2 has survived its closest approach to the black hole as a compact, unresolved source at L’ 

Observations SgrA* G2 Periapse passage: spatially unresolved ➡ disentangle 

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closest approach(Mar.16.2014) 

G2 is fully consistent with a point source 

Result 2 G2’s L’ brightness measurements are consistent with those over the last decade 

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Result 3 G2’s motion continues to be consistent with a Keplerian model. 

consistent with predictions of their orbital model 

Conclusion G2 has an central star of ∼30 L⊙ , and is surrounded by a thick dust shell 

Br-γ VS L’ emission Trace hot gas externally heated by ionizing photons Tidal interaction with the BH Only SOME gas associated with G2 has a size that exceeds its tidal radius Specially unresolved Continues to follow a well- defined Keplerian orbit Constant in brightness Come from a dust shell surrounding an underlying star 

Line 1: G2 has central stellar source •The L’ flux has been invariant at ∼ 2.1 mJy •In 2004, G2 had an L’ - M’ color of ∼ 0.3, which corresponds to a blackbody temperature of ∼ 560 K. • •No K’ detection has been made in any epoch. •The L’ emission is much more compact than the emission in Br-γ, and thus originates in a different region. 
 

Large size? binary merger! 

Line 2: G2 is a merger product • Tidal radius arguments • Tidal radius of the source has not become smaller than the source size for most of the time • For MBH = 4.3E6M⊙, the tidal radius is : 

Time development of the tidal radius Derived L’ size of G2(2.6AU): consistent with observation 

Br-γ VS L’ emission The Br-γ emission is a by-product of the tidal interaction, whereas the L’ emission traces the properties of the merger product. 

Future research… • Merger product • Eccentric orbit • S-star cluster • Is it possible that an important fraction of the S- stars has resulted from such mergers?