MASS FUNCTION OF STELLAR REMNANTS IN THE MILKY WAY (pron: Woocash Vizhikovsky) Warsaw University Astronomical Observatory Wednesday Seminar, IoA Cambridge, 8 July 2015
COLLABORATORS Krzysztof Rybicki (PhD student) Zuzanna Kostrzewa-Rutkowska OGLE team in Warsaw Gaia Alerts team in Cambridge
STELLAR REMNANTS Remnants are the products of the final stages of stellar evolution Brown Dwarfs, White Dwarfs, Neutron Stars, Black Holes Problem: most remnants are dark - very hard to find!
STELLAR REMNANTS Masses of Neutron Stars (from binaries) - narrow peak around 1.5 MSun (e.g.,kiziltan+2013) Masses of Black Holes (from binaries) - separate peak from ~6 MSun (e.g., Ozel+2010) but no gap between NS and BHs from stellar evolution synthesis and supernovae explosions (e.g., Fryer&Kalogera 2001)
MICROLENSING Gravitational lensing by compact lenses (stellar or remnants) Sources: background stars (chance: 10-6 in the Bulge, 10-8 in the LMC) ~1 month astrometry (centroid motion) animations by S.Gaudi photometry (sum of images) ~1mas
MICROLENSING About 20% of microlensing events should be due to stellar remnants (Gould 2000) 17% WD 3% NS 0.8% BH 2000 events found every year -> 16 black holes!!! so, why not found yet? Microlensing event rate for different lens populations (Gould 2000) -
MICROLENSING mass of the lens from microlensing 1 M = [te (µl µs )] 2 1 DL 1 DS constant Einstein Ring crossing time proper motions lens and source distances lens and source the only parameter measured from a standard microlensing event
MICROLENSING to compute the mass of the lens we need both: - Einstein Radius (theta_e) - microlensing parallax (pi_e): high amplification events E M= E astrometry Earth parallax space-based parallax (e.g., Earth-Spitzer)
OPTICAL GRAVITATIONAL LENSING EXPERIMENT (OGLE) photo (c) K.Ulaczyk & Ł.Wyrzykowski dedicated 1.3m telescope since 1996 in Las Campanas Obs. Chile
OGLE-IV SKY since 2010 Microlensing and Variable Stars Bulge half-billion stars down to 21mag Cadence: red ~30 epochs/night yellow ~10 epochs/night green ~3 epochs/night blue ~1 epoch/night cyan ~1 epoch /2 nights Variables and Transients Magellanic System (LMC+MBR+SMC) 700 sq.deg. limit: 22 mag in I-band cadence: 2-5 nights
5 MILLION STARS EVERY 3 MINUTES FoV 1.4 sq.deg., mag limit 21 mag in I-band
SEARCH FOR LENSING REMNANTS OGLE-III: 2001-2009 150 millions of stars in the Bulge 3500 standard events (Wyrzykowski+2015) 65 high quality parallax events 25 events with P>50% having a remnant (dark) lens 11 events with P>75% having a remnant (dark) lens 3 BH lens candidates (P>99% remnant) Wyrzykowski+2015
BH CANDIDATES OGLE-III event name BLG156.8.68730 te [d] Mass [M ] Distance [kpc] 287 12.7+35.9-7.0 3.4+7.8-1.0
BH CANDIDATES OGLE-III event name BLG333.2.53483 te [d] Mass [M ] Distance [kpc] 172 4.1+10.8-1.8 3.3+7.5-0.8
BH CANDIDATES the longest microlensing event ever! 7 years of lensing OGLE-III event name BLG205.3.159237 te [d] Mass [M ] Distance [kpc] 256 6.9+17.7-3.0 2.1+5.0-0.6
MASS FUNCTION assuming proper motions for sources in the bulge and lenses in the disk individual events mass probability distribution functions P>50% (orange+blue) and P>75% (red+green) of being a dark remnant
MASS FUNCTION Finding most probable mass distribution for our samples of remnant events (50% and 75%) broad single gaussian gauss+exp: no gap between NSs and BHs? simulations indicate that we should see the gap in our data if present
MICROLENSING to compute the mass of the lens we need both: - Einstein Radius (theta_e) - microlensing parallax (pi_e): high amplification events E M= E astrometry Earth parallax space-based parallax (e.g., Earth-Spitzer)
1700deg2 Disk Fields Bulge and Sgr dsph Fields Supernovae Search Fields LMC and SEP Gaia figure by Nadia Blagorodnova, OGLE fields by Jan Skowron OGLE-GAIA SKY
MICROLENSING WITH GAIA+OGLE parallax events from 2014 and 2015 also observed by Gaia predicted Gaia astrometric observations for the most probable mass Rybicki+ in prep.
MICROLENSING WITH GAIA+OGLE Simulated Gaia astrometry for on-going OGLE parallax events Gaia astrometry expected at <0.1mas level (at the end of the mission) Lens mass recovery at a level of 0.1-0.2 MSun see also Belokurov and Evans (2002)
ON-GOING CANDIDATE BH EVENT ogle.astrouw.edu.pl/ogle4/ews/ews.html OGLE event name OGLE-2014-BLG-0613 te [d] Mass [M ] Distance [kpc] 530 7.5+19.8-3.4 1.6+4.2-0.6
SUMMARY there should be dozens of microlensing events due to stellar remnants we found at least 3 strong BH candidates among 65 parallax events found among 150 million stars monitored by OGLE-III 2001-2009 total of 11/25 dark remnant lenses mass distribution does not support NS-BH mass gap astrometric data from Gaia combined with OGLE photometry will constrain masses of remnant lenses to 0.1 MSun
THANK YOU!
TESTING THE ASSUMPTIONS Bulge-Disk and sources at 8kpc Sources at 4kpc instead of 8kpc Bulge-Bulge lensing
CANDIDATES Bennett+2001 X-rays - no signal Maeda et al. 2005 and Nucita et al, 2006