  Hexagonally deformed Fermi surfaces and strong nesting, found in topological
insulators (TIs) such as $Bi_2Se_3$ and $Bi_2Te_3$, have led to several
predictions of the existence of Density Wave order in these systems. Recent
evidence for strong Fermi surface nesting in superconducting $Cu-Bi_2Se_3$ and
$Nb-Bi_2Se_3$ has further led to speculation about the importance of charge
order in the context of unconventional superconductivity. Here, we report the
first observation of a novel anomaly in $Bi_2Se_3$ at 140K, which may be
associated with a Charge Density Wave (CDW)-like transition. This transition
was identified from both structural and electronic measurements, where: a) a
periodic lattice distortion at above room temperature was characterized as a
diffuse charge order in $Bi_2Se_3$ between \vec{k} and
\vec{k}\pm\mathrm{\Delta}\vec{k} from electron diffraction; and b) an opening
of energy gap signatured with metal-to-insulator like transition at 140K was
identified from resistivity vs temperature measurement. This is further
corroborated by nuclear magnetic resonance (NMR) studies of the spin-lattice
relaxation ( $\frac{1}{T_1}$) rate of the $^{209}Bi$ nucleus, which also
displays a transition at 140K associated with an opening of an energy gap of
~8meV. Additionally, we also observe another anomaly in $\frac{1}{T_1}$ near
200K, which appears to display anisotropy with the direction of the applied
magnetic field.
